Further studies on cucumber mosaic virus infection of narrow-leafed lupin (Lupinus angustifolius): seed-borne infection, aphid transmission, spread and effects on grain yield

Four field trials were done with narrow-leafed lupins (Lupinus angustifolius) in 1988 - 1989, to examine the effect of sowing seed with 5% and 0.5% cucumber mosaic virus (CMV) infection on subsequent virus spread, grain yield and percentage of infection in harvested seed. A proportion of the CM V-infected seed failed to produce established plants and thus, plots sown with 5% and 0.5% infected seed contained 1.5-2.9% and 0.2-0.3% of seed-infected plants respectively. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity in plots sown with 5% infected seed than with 0.5% infected seed. In three trials, sowing 5% infected seed resulted in yield losses of 34 - 53% and CMV infection in the seed harvested of 6 - 13%. The spread of CMV infection resulting from sowing 0.5% infected seed did not significantly decrease yield. However, late CMV spread in these plots caused > 1% seed infection. In the fourth trial, which was badly affected by drought, CMV spread only slowly, there was no significant effect of CMV on grain yield and the percentage of infected seed harvested was 3–5 times less than that in the seed sown. When CMV-infected seed was sown at different depths, target depths of 8 and 11 cm decreased the incidence of seed-infected plants by c. 15% and c. 50% respectively compared with sowing at 5 cm. However, in glasshouse tests, treatment with the pre-emergence herbicide simazine failed to selectively cull out seed-infected plants. The field trials were colonised by green peach (Myzus persicae), blue-green (Acyrthosiphon kondoi) and cowpea (Aphis craccivora) aphids. When the abilities of these aphid species and of the turnip aphid (Lipaphis erysimi) in transmitting CMV from lupins to lupins were examined in glasshouse tests, short acquisition access times favoured transmission. With 5–10 min acquisition access times, overall transmission efficiencies were 10.8%, 9.4%, 6.1% and 3.9% for the green peach, cowpea, blue-green and turnip aphids respectively.     

Losses in productivity of subterranean clover swards caused by sowing cucumber mosaic virus-infected seed

Field trials were done in 1988 - 89 at two sites to examine the effects of sowing seed stocks in which a low proportion (1.6–7.0%) of the seed was carrying cucumber mosaic virus (CMV) infection (= infected seed) and the subsequent CM V spread that results, on the productivity of swards of subterranean clover cvs Esperance, Green Range and Karridale. Except in irrigated plots of cv. Green Range, a variable proportion of the CMV-infected seedlings always failed to establish, so sowing infected seed normally resulted in plots containing fewer or far fewer seed-infected plants than expected. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity when the plots contained more seed-infected source plants. In two irrigated trials at South Perth, in which healthy and infected seed of cvs Esperance and Green Range was sown, CMV spread was extensive. When the plots were left undefoliated, herbage dry wt yields were decreased by 12 – 30% and seed yields by 53 – 64% due to infection. When they were mown, the herbage dry wt losses recorded were 17 – 24%. In three trials at Mt Barker sown with healthy and infected seed, extensive spread of CMV occurred with cv. Green Range but not with cvs Esperance and Karridale. With cv. Green Range, losses of 25 – 28% in herbage dry wt were recorded inside CMV-affected patches in mown or grazed plots, while losses were up to 13% when herbage was sampled at random. Seed yield losses were 40–42% and 53% in infected mown and undefoliated cv. Green Range plots, respectively. In the mown or grazed plots of cvs Esperance and Karridale, herbage dry wt losses recorded were up to 7% while seed yield losses were 9 – 16% in mown and 9% in undefoliated plots. The mean wt/seed of seed harvested from mown plots of cvs Green Range and Karridale sown with infected seed was 8–12% less than that of seed from mown control plots. CMV was detected in seed harvested from undefoliated cv. Green Range plots and mown plots of cvs Green Range and Karridale sown with infected seed but levels of seed infection with the mown plots were 3–5 times less than in the seed sown. Field trials were done at two sites in 1987 – 90 to examine the persistence of CMV in subterranean clover swards. CMV infection was established in 1987 and the plots were grazed in subsequent years. At Badgingarra, infection gradually decreased with little CMV being recovered by 1990. At Mt Barker, recovery of CMV was relatively poor in 1988 and even poorer in 1989, but there was some resurgence of CMV infection in 1990.     

Interactions between a seed-borne strain of cucumber mosaic cucumovirus and its lupin host

The relationship between time of inoculation with cucumber mosaic cucumovirus (CMV) and the growth, seed production and rate of seed transmission of virus in lupin (Lupinus angustifolius cv. Illyarrie) was studied in field-grown plants. Plants inoculated at the seedling stage (2 days post-emergence) showed 45% mortality. Plants infected through the seed were more stunted than plants inoculated at the seedling stage. Plants inoculated up to the mid-vegetative growth stage (58 days post-emergence) yielded ≤ 27% of the dry matter and ≤ 9% of the seed of healthy plants. Late inoculation (114 days post-emergence) did not affect dry matter yield, but reduced seed yield to 75% of that of healthy plants. Rate of seed transmission depended on the time of inoculation of plants. The maximum rate was 24.5% for plants that were inoculated at the mid-vegetative growth stage (58 days post-emergence). However, early inoculation caused a large reduction in seed yield, and it was shown that plants inoculated at the beginning of flowering (94 days post-emergence) produced greater numbers of infected progeny than plants inoculated at earlier or later times. No relationship was observed between seed weight and transmission of CMV. Infectious CMV was recovered from the embryo, but not from the testa. A simple seed transmission model was used to evaluate several hypothetical epidemics and to determine the time of inoculation which results in greatest rates of seed transmission of CMV. For example, when fewer than 73% of plants in a crop become infected with CMV, then the rate of transmission of virus in crop seeds will be greatest when inoculations are at the beginning of flowering.     

Biological properties of necrotic and non-necrotic strains of bean yellow mosaic virus in cool season grain legumes

A collection of 51 bean yellow mosaic virus (BYMV) isolates was transmitted from infected Trifolium subterraneum (subterranean clover) to Lupinus angustifolius (narrow‐leafed lupin) by Myzus persicae (green peach aphid). Depending on isolate and L. angiistifolius genotype used, two distinct responses developed in L. angustifolius plants, either systemic necrosis and plant death or non‐necrotic reactions of varying severity. Ten isolates caused necrosis and plant death in cv. Danja. However, when nine of these were inoculated to breeding line 90L423‐07‐13, seven induced non‐necrotic reactions, while two caused necrosis and plant death. Thirty seven isolates always produced non‐necrotic reactions regardless of genotype of L. angustifolius inoculated. Non‐necrotic and necrotic isolates originally came both from lupins and other species, and the non‐necrotic isolates were no less efficiently transmitted by M. persicae than the necrotic ones. When one isolate of each type was inoculated together to T. subterraneum and nine months later this culture was used as an acquisition source for aphid transmission to L. angustifolius, only the necrotic type was detected. Previous infection of L. angustifolius plants with a non necrolic isolate prevented subsequent infection by a necrotic one. All necrotic and non‐necrotic isolates reacted with BYMV antiserum in ELISA but only two cross‐reacted with antiserum to clover yellow vein virus (CYVV). When selected necrotic and non‐necrotic isolates were inoculated to differential hosts, all behaved like BYMV and not CYVV. When three isolates of each type were transmitted to 11 other cool season grain legume species, except in Cicer arietinum (chickpea), there were no necrotic reactions, but symptom severity varied with the isolate and species inoculated. The two isolates that caused necrosis in C. arietinum did not do so in L. angustifolius. The six isolates from Vicia faba (faba bean) all caused non‐necrotic reactions in L. angustifolius cv. Danja and 90L423‐07‐13. These and two necrotic isolates readily infected five genotypes of V. faba always causing severe symptoms. However, three non‐necrotic isolates from L. angustifolius and a further necrotic isolate were poorly infectious on V. faba in which they generally induced mild symptoms. These results show that at least three strain groups of BYMV can be distinguished by their reactions in different L. angustifolius genotypes, one causing necrosis and death in cv. Danja and 90L423‐07‐13, one causing necrosis and death in Danja but not 90L423‐07‐13, and one causing non‐nccrotic reactions in both. These strain groups could not be distinguished when representative necrotic and non‐necrotic isolates were inoculated to other grain legume species. However, inoculation to V. faba distinguished two other BYMV strain groupings differing in severity of symptoms and ability to infect this species.     

Patterns of spread of two non-persistently aphid-borne viruses in lupin stands under four different infection scenarios

Patterns of spread of Bean yellow mosaic virus (necrotic type, BYMV‐N) and Cucumber mosaic virus (CMV) were examined in stands of narrow‐leafed lupin (Lupinus angustifolius) where naturally occurring aphid vectors moved them from external or internal primary virus sources. The lupin stands were: commercial crops near BYMV‐infected clover pasture with or without an intervening non‐host barrier crop; a large rectangular block with BYMV‐N and CMV sources on opposite sides and a narrow, non‐host barrier crop facing the BYMV‐N source; and a plot within which seed‐infected lupin plants acted as internal CMV sources. When BYMV‐N spread into commercial crops in the absence of a non‐host barrier, there was a steep decline in its incidence with distance from the crop edge. However, when a 20 m‐wide perimeter barrier of oats intervened between the two, there was only a shallow decline. When CMV and BYMV‐N spread from opposite directions into a block with a 0.25 m‐wide oat barrier between it and the BYMV‐N source, the BYMV‐N incidence gradient was shallow but in the opposite direction the CMV gradient was steep. When CMV spread from primary sources within a plot, infection was concentrated in large internal patches. Spread of BYMV‐N was more diffuse with more isolated symptomatic plants and small clusters than occurred with CMV, spread of which was more comprehensive, reacting the near monocyclic and polycyclic patterns of spread with BYMV‐N with CMV respectively. Spread of both viruses was greater along than across rows, especially with CMV. With BYMV‐N, three different phased cycles of secondary spread were evident in the individual symptomatic plants within the small clusters that formed away from the edges of lupin stands. These findings help validate inclusion of perimeter non‐host barriers within an integrated disease management strategy for BYMV‐N in lupin.     

Varying phosphorus supply and development,growth and seed yield in narrow-leafed lupin

Narrow-leafed lupin (Lupinus angustifolius L.) is usually grown in sandy, acidic and phosphorus (P) deficient soil with low yield and variable harvest index. This study aimed to examine the effects of varying P supply on lupin growth, seed yield and harvest index. Non-abscission plants (cv. Danja) were grown in Lancelin sand at seven rates of P supply (5, 10, 15, 20, 25, 30 or 40 mg kg^–1) in a naturally-lit glasshouse. The rate of leaf emergence, flowering time and flower number were decreased or delayed by low P supply (5, 10 or 15 mg kg^–1), with no differences at P rates higher than 20 mg kg^–1. High P supply (25, 30 or 40 mg kg^–1) increased plant seed yield and harvest index largely by increasing the number of pods and consequently yield on the lateral branches, but had less effect on the number of seeds per pod and seed size. Seed yield and seed P concentration continued to increase up to 40 mg P kg^–1but harvest index plateaued at 25 mg P kg^–1, indicating that low P supply decreased reproductive growth more than vegetative growth in narrow-leafed lupin.     

Interactive effect of cytokinin and potassium on sink-source relationships in Lupinus angustifolius

This study examined whether increased K supply in conjunction with BAPcould increase lupin seed yield and harvest index by enlarging sink volume (podnumber), increasing assimilate and improving assimilate partitioning to filltheadditional pods induced by BAP treatment. Narrow-leafed lupin(Lupinusangustifolius, cv. Danja abs^– mutant) was grown inaglasshouse, in pots containing sandy soil with four K treatments (0, 15, 60 and120 mg K/kg soil). BAP (2 mM) was applied daily toallmain stem flowers throughout the life of each flower from opening to senesced.BAP application did not affect assimilate production (as measured by totalabove-ground biomass), but changed assimilate partitioning. On BAP-treatedplants, there were greater proportions of seed to pod wall dry weight on themain stem but smaller proportions on the branches, and an increased weightratioof seed to pod wall overall which meant more assimilate was used for seedgrowthrather than pod wall growth. BAP increased the number of pods per plant by35% and this more than compensated for the decreases in seeds per podandseed weight. Therefore, there was an increased harvest index (+11%)and seed yield per plant (+13%) in BAP-treated plants. BAP alsoincreased the number of pods with filled seeds (146%) on the main stemand main stem seed K⁺ concentration (from 0.81% to0.87%). Added K increased biomass but only slightly affected assimilatepartitioning. As applied K increased, relatively more assimilate was used forpod wall growth rather than seed growth. Added K increased seed yield per plantby about 14% due to increases in seed weight and the number of pods onthe main stem. Moreover, K⁺ concentration in seeds and shootsincreased with increasing level of applied K. Seed yield was enhanced more byBAP when K was supplied at high levels. Increasing K supply interactedpositively with added BAP by increasing narrow-leaf lupin seed yield andharvestindex through increases in assimilate supply and its partitioning into seeds.     

Reflective mulch decreases the spread of two non-persistently aphid transmitted viruses to narrow-leafed lupin (Lupinus angustifolius)

Trials were done in 1987–1989, to investigate the effect of a reflective aluminium painted polythene mulch in protecting rows of narrow-leafed lupin ( Lupinus angustifolius ) from infection with two non-persistently aphid-transmitted viruses, bean yellow mosaic (BYMV) and cucumber mosaic (CMV). The mulch greatly decreased the rate and extent of spread of BYMV from external sources into mulch-protected rows in two trials, but was somewhat less effective in a third. The rate and extent of spread of CMV from an adjacent external source into reflective mulch-protected rows was also greatly decreased in one trial in which the mulch also decreased spread within rows and was effective even when the primary infection source was only 2.5 m away. In a trial sown with CMV-infected seed ( c . 2% seed transmission), the mulch decreased CMV spread from primary foci within rows. Reflective mulch can be used to protect breeders' single row plots of lupins from infection with CMV and BYMV.     

Redistribution of Manganese in Maturing Lupin us angustifolius cv. Illyarrie in Relation to Levels of Previous Accumulation

The retranslocation of Mn from pools of pre-accumulation todeveloping seed of Lupinus angustifolius was examined in growthchamber and field experiments. In the growth chamber experiment, plants (cv. Illyarrie) weregrown in sand containing Mn at 18 levels of supply from low(15 fig Mn kg"1) to luxury (12800 fig Mn kg{small tilde}l).At 90 d, sand was washed from the roots and the plants weregrown to maturity in nutrient solution in the absence of Mn.At sequential harvests, the plants were divided into a numberof fractions and were analysed for Mn to determine changes inthe amount of Mn contained in each component. Plants (cv. Marri)were also grown in the field at a Mn deficient site with andwithout added Mn, and similar harvests and observations weremade. Manganese moved readily from roots, stems and petioles to developingsinks, including seeds via pods. Retranslocation of Mn preventedthe appearance of Mn deficient seed (‘split seed’)in plants which had accumulated sufficient Mn prior to the omissionof Mn supply. The mode of Mn transport is discussed, and itsconveyance to seed in phloem, mediated by transfer cells, issuggested. The identification of pools of Mn accumulation fromwhich Mn may retranslocate presents a basis on which tests prognosticof impending Mn deficiency in maturing lupins may be developed.Stem is favoured as the tissue on which to base such tests. No Mn translocated to developing seed sinks from mature, oreven senescing lupin leaves. The cause appears to be that Mnis poorly loaded into the phloem of leaves although much wasfound to be leachable. About 40 per cent of leaf Mn was extractablewith water, more (approx. 70 per cent) with dilute ethylenediamine tetraacen’c acid but little (approx. 14 per cent)with N7>Jdimethyl formamide along with other cell contents.The form of Mn in leaves is discussed.     

Seed-borne cucumber mosaic virus infection of subterranean clover in Western Australia

In Western Australia, infection with cucumber mosaic virus (CMV) was widespread in all three subspecies of subterranean clover (Trifolium subterraneum) growing in plots belonging to the Australian National Subterranean Clover Improvement Programme. Seed-borne CMV was detected in seed harvested in 1984–1986 of 18/25 cultivars from two collections of registered cultivars; seed transmission rates ranged up to 8.8%. Seed samples from CMV-inoculated plants of 11 cultivars transmitted the virus to 0.5–8.7% of seedlings. Seed transmission rates greater than 5% were obtained only with cvs Enfield, Green Range and Nangeela. CMV was not detected in seed harvested in 1975–1981 from one of the registered cultivar collections, in 17 commercial seed stocks from 1986 or in a survey of subterranean clover pastures.
Symptoms in subterranean clover naturally infected with CMV included mottle, leaflet downcurling and dwarfing but severity varied with cultivar and selection. CMV isolates from different sources varied in virulence when inoculated to subterranean clover; two (both from subterranean clover) were severe, two moderate and three (including one from subterranean clover) mild. In pot tests, CMV decreased herbage production and root growth (dry wts) of cv. Green Range by 49% and 59% respectively. In spaced-plants growing in plots, CMV decreased herbage production and root growth of cvs Green Range and Northam by 59–630 and seed production of cv. Green Range by 45%. In rows sown with infected seed, aphid spread increased infection levels to 75% in cv. Green Range and 44% in cv. Esperance and losses in herbage production of 42% and 29% respectively were recorded.
CMV isolated from subterranean clover included isolates from both serogroups.     

Virus diseases of garden lupin in Great Britain

Two viruses occur widely in lupins in Britain. Alfalfa mosaic virus (AMV), of which two strains were isolated, was found mainly in named Russell varieties. Lupin mottle virus (LMV), a previously undescribed strain of the bean yellow mosaic virus (BYMV) common pea mosaic virus (CPMV) complex, was found more commonly in seedling lupins. Cucumber mosaic virus (CMV) was isolated once. The AMV strains were differentiated by their reaction in Phaseolus vulgaris; they were serologically closely related. Both AMV and LMV were aphid transmitted but not transmitted in lupin seed. LMV was distantly serologically related to both BYMV and CPMV. It cross-protected against BYMV but not against CPMV and it differed from both these viruses in some host reactions. The CMV isolate from lupins was similar to type CMV. It was transmitted both mechanically and by aphid, easily from cucumber to cucumber, but with difficulty from cucumber to lupin.     

Effects of seed manganese concentration on lupin emergence

Seed of narrow-leafed lupin (Lupinus angustifolius L.) produced in Western Australia often has low manganese (Mn) concentration because of low Mn availability in the soil during grain filling. A major problem of lupin production is poor seedling establishment. We tested the hypothesis that low Mn concentration in lupin seeds decreases emergence.The experiment was a factorial design comparing emergence of lupins (cv. Gungurru) grown under glasshouse conditions from seed with 2 different internal Mn concentrations (7 or 35 mg Mn kg^–1 DW) and with 2 external Mn fertiliser treatments (0 or 10 mg MnSO₄.H₂O kg^–1 soil). There were no visible differences between the seeds. Emergence was monitored and plants were harvested 17 days after sowing.Emergence was approximately 60% in all pots sown with low Mn compared to 100% in pots sown with high Mn seed. Application of Mn did not increase the final emergence of low Mn seed. Seed viability was assessed by staining with tetrazolium chloride, a common test used in seed testing laboratories. All high Mn seed were viable while 34% of low Mn seed were completely or partly unstained and therefore were non-viable. We have shown that low Mn supply during seed filling may lead to production of non-viable seed that cannot be visually distinguished from viable seed..     

Determining the relative roles of different aphid species as vectors of cucumber mosaic and bean yellow mosaic viruses in lupins

Glasshouse and field studies were done to determine the relative roles of different colonising and non-colonising aphid species as vectors of two non-persistently transmitted viruses, cucumber mosaic cucumovirus (CMV) and bean yellow mosaic potyvirus (BYMV) in narrow-leafed lupin (Lupinus angustifolius) crops in Australia. The abilities of nine different aphid species in transmitting CMV from infected to healthy lupins and BYMV from infected subterranean clover to healthy lupins were compared in the glasshouse using 5–10 min acquisition access feeds. The percentage transmission efficiencies found with lupin-colonising aphid species were (CMV/BYMV): Acyrthosiphon kondoi (6/15), Aphis craccivora (10/14) and Myzus persicae (11/77). With non-colonising species the respective efficiencies were: Brachycaudus rumexicolens (0.9/0), Lipaphis erysimi (4/8), Rhopalosiphum maidis (9/6), R. padi (5/5), Sitobion miscanthi (2/11) and Therioaphis trifolii (4/5). When flying aphids were trapped in the field in four successive years (1993–1996) on vertical nets downwind of virus-infected lupins, 13 different species were caught at a “wheatbelt” site and 18 at an urban irrigated site. Of 2833 aphids caught at the “wheatbelt” site, 64 transmitted CMV to lupin test plants. At the irrigated site, numbers of aphids transmitting CMV/numbers caught were 12/186 while the corresponding numbers for BYMV were 11/727. M. persicae, A. kondoi and R. padi transmitted both viruses, while additional vectors of CMV found were A. craccivora, Acyrthosiphon pisum, B. rumexicolens, L erysimi, R. insertum, T. trifolii and Toxoptera citricidus. Averaged over four years, A. kondoi accounted for 50% of CMV transmissions at the “wheatbelt” site, M. persicae for 16% and R. padi for 22%, and these three species were caught in the greatest numbers, comprising 28%, 13% and 37% respectively of the total catch. At the irrigated site R. padi accounted for half the CMV transmissions, while R. padi and A. kondoi together accounted for most of the BYMV transmissions. R. padi, A. kondoi, M. persicae and T. citridus were the most common aphid species at this site. These findings suggest that M. persicae, A. kondoi and R. padi are the aphid species likely to be most important as vectors of CMV and BYMV in narrow-leafed lupins grown in mediterranean-type climatic zones of southern Australia.     

Density Studies on Lupins. II. Components of Seed Yield

Components of seed yield of cv. Ultra (Lupinus albus L.) andcv. Unicrop (L. angustifolius L.) were measured when grown atthree densities. The low density (10 plants m^–2) Unicropyield (34 g seed per plant) was 1.8 times that of Ultra as ithad more branches, pods and seeds per pod. Ultra seeds (310mg per seed) were heavier than Unicrop seeds (180 mg). The branchingpattern of Ultra was less dependent on plant density, henceat 93 plants m^–2 it gave a higher per plant yield (7.4vs 6.4 g) than Unicrop at lower densities (83 plants m^–2).Density had most influence on pod formation and only small effectson seeds per pod and seed weight. Yield components on the main-steminflorescence were influenced less by density than componentson branch inflorescences. Later formed, higher order generationsof inflorescences were most affected by increased inter- andintra-plant competition. Pod numbers on the main-stem were similarfor both species. Pods formed at higher flower nodes in Unicrop,but the lower flower nodes were less fertile than those in Ultra.Node position of flowers had no influence on seed set in main-stemUnicrop pods, but pods from higher nodes in Ultra formed fewerseeds. Seed weights in Unicrop were similar among main-stemnodes but in Ultra seed weights tended to increase at highernodes. Lupinus spp, lupins, seed yield, planting density     

Effects of cereal borders, admixture with cereals and plant density on the spread of bean yellow mosaic potyvirus into narrow-leafed lupins (Lupinus angustifolius)

In studies of virus control measures, field experiments in 1987–1991 investigated the effects of cereal and fallow borders, admixture with cereals and plant density on spread of bean yellow mosaic potyvirus (BYMV) from pastures dominated by subterranean clover (Trifolium subterraneum) into plots of narrow-leafed lupins (Lupinus angustifolius). Virus spread was mainly monocyclic because BYMV killed infected lupin plants and between systemic movement and death there was only a brief period for BYMV acquisition and transmission to other plants by vector aphids. In plots with cereal borders, the rate and extent of BYMV spread into the lupins was decreased; at final assessment the numbers of infected plants were 43–60% less than in plots with fallow borders. Admixture with cereals also decreased the rate and extent of BYMV spread into lupin plots, numbers of infected plants being decreased by 76–96% at the time of final assessment. When lupins were sown at different seeding rates to generate a range of plant densities and weeds were removed, high densities decreased BYMV infection. The higher incidences of BYMV infection in sparse stands were attributed partly to smaller plant numbers and partly to incoming viruliferous vector aphids being more attracted to plants with bare earth around them, than to a plant canopy. BYMV infection decreased grain yield of samples from infected lupin plants by 94–100%. In plots with 34% infection and sparse stands, grain yield was decreased by about one third. Plotted progress curves for the accumulated numbers of alate aphids of the BYMV vector species Acyrthosiphon kondoi and Myzus persicae resembled those for numbers of BYMV infected plants in 1990, but in 1991 only the curve plotted for M. persicae did so. There was a 2 week delay between the curves for aphid numbers and virus counts which reflected the time taken for obvious systemic necrotic symptoms to develop in lupins.     

Electronically monitored cowpea aphid feeding behavior on resistant and susceptible lupins

The feeding behavior of cowpea aphid, Aphis craccivora Koch (Homoptera: Aphididae) was examined on seedlings of narrow leafed lupin, Lupinus angustifolius L., and yellow lupin, L. luteus L., using electronic monitoring of insect feeding behavior (EMIF). Aphid feeding behavior was first compared between resistant (cv. Kalya) and susceptible (cv. Tallerack) varieties of narrow-leafed lupin. Aphids spent significantly more time in non- penetration and stylet pathway activities, and significantly less time in the sieve element phase on Kalya than on Tallerack, suggesting that feeding deterrence is an important component of aphid resistance in Kalya. Aphid feeding on a susceptible yellow lupin variety (cv. Wodjil) was then compared with that on two resistant lines, one (Teo) with high and the other (94D024-1) with low seed alkaloid content. There were no consistent differences in aphid feeding behavior between Wodjil and Teo. Total, mean and percentage sieve element phase times were significantly lower, and total and percentage times in non-phloem phase were greater on 94D024-1 than on Wodjil, suggesting the possibility of phloem-based deterrence in 94D024-1.     

Potassium nutrition effects on seed alkaloid concentrations,yield and mineral content of lupins (Lupinus angustifolius)

To ensure that narrow-leafed lupin (Lupinus angustifolius L.) meets feed quality standards, the concentration of alkaloids must be kept under the maximum acceptable limit of 200 mg kg^–1 DM. One of the factors that may affect seed alkaloid concentration is soil nutrient deficiency. In this paper, we report the results of glasshouse and field experiments that tested the effect of potassium (K) deficiency on seed alkaloid concentrations. In the glasshouse, seed alkaloid concentrations increased by 385, 400 and 205% under severe K deficiency in sweet varieties (Danja, Gungurru and Yorrel, respectively) of L. angustifolius. The concentration of alkaloids in Fest, the bitter variety, was always high regardless of soil K status. At all levels of applied K (0–240 mg kg^–1 soil), lupanine was the predominant alkaloid in sweet varieties, whereas 13-hydroxylupanine prevailed in the bitter variety. Seed yield of all varieties increased exponentially with increasing amounts of applied K, reaching a maximum at 60 mg K kg^–1 soil. In the field, application of K to deficient soils decreased seed alkaloid concentration at Badgingarra, Western Australia (WA) but not at Nyabing, WA, in 1996. In both field trials, seed yield and mineral content were not affected by the amounts of K fertiliser applied. These findings highlighted the need for adequate K fertilisation of deficient soils in WA to avoid the risk of producing low quality lupin seed with high alkaloid concentrations. K deficiency is involved in stimulating alkaloid production in sweet varieties of L. angustifolius.     

Natural resistance to cucumber mosaic virus in lupin species

Ten species of lupins (Lupinus spp.) were tested for resistance to cucumber mosaic cucumovirus (CMV) in field experiments where inoculation was by naturally-occurring aphid vectors, and in the glasshouse by sap or graft-inoculation. L. albus and six species of ‘rough-seeded’ lupins did not become infected with CMV either under intense inoculum pressure in the field or when graft-inoculated. Two L. hispanicus, 17 L. luteus and four L. mutabilis genotypes became infected with CMV in the field, but no infection was detected in L. hispanicus P26858 or seven L. luteus genotypes. CMV was detected at seed transmission rates of 0.2–16% in seedlings of infected L. luteus, differences in levels of seed transmission between genotypes being significant and relatively stable from year to year. Graft-inoculation of CMV to plants of six genotypes of L. luteus in which no infection was found in the field induced a systemic necrotic reaction suggesting that the resistance they carry is due to hypersensitivity. In L. hispanicus accessions P26849, P26853 and P26858, CMV sub-group II isolate SN caused necrotic spots in inoculated leaves without systemic movement, while sub-group I isolate SL infected them systemically without necrosis. Another sub-group I and two other sub-group II isolates behaved like SL in P26849 and P26853 but infected only inoculated leaves of P26858. This suggests that two strain specific hypersensitive resistance specificities are operating against CMV in L. hispanicus. When plants of L. luteus genotypes that gave hypersensitive reactions on graft-inoculation were inoculated with infective sap containing two sub-group I and seven sub-group II isolates, they all responded like L. hispanicus P26858. A strain group concept is proposed for CMV in lupins based on the two hypersensitive specificities found: strain group 1 represented by isolate SN which induces hypersensitivity with both specificities, strain group 2 represented by the three isolates which induced hypersensitivity only with the specificity present in L. luteus and L. hispanicus P26858, strain group 3 by as yet hypothetical isolates that induce hypersensitivity only in presence of the specificity in L. hispanicus P26849 and P26853 that responded just to isolate SN, and strain group 4 by isolate SL which overcomes both specificities. When F₂ progeny plants from crosses between hypersensitive and susceptible L. luteus parents were inoculated with isolate SN, the resistance segregated with a 3:1 ratio (hypersensitive:susceptible), suggesting that a single dominant hypersensitivity gene, Ncm-1, is responsible. As gene Ncm-1 had broad specificity and was not overcome by any of the five CMV isolates from lupins tested, it is valuable for use in breeding CMV resistant L. luteus cultivars.     

Seed-borne alfalfa mosaic virus infecting annual medics (Medicago spp.) in Western Australia

Infection with alfalfa mosaic virus (AMV) was widespread in introduction, evaluation and seed increase plots of cultivars and numbered selections of annual medics (Medicago spp.) in Western Australia; the virus was detected in plots of seven species. When seed stocks from the West Australian annual medic collection harvested in 1984–1986 were sown and seedlings tested, seed-borne AMV was found in all 12 cultivars and in 44/50 numbered selections, belonging to 10 species. Seed transmission rates to seedlings ranged from 0.3–74% and exceeded 5% in 33 seed lots. By contrast, when seedlings of four species grown from seed harvested in 1971–1978 were tested, no AMV was detected; the oldest infected seed stock found was from 1980. In commercial seed stocks of two cultivars released in 1987, the levels of seedling infection with AMV found were 0–0.2% for M. polymorpha cv. Santiago and 526% for M. murex cv. Zodiac. In commercial 1986 seed of M. polymorpha cvs Serena and Circle Valley, AMV was detected in 3/13 and 6/9 stocks respectively; transmission rates to seedlings in infected stocks were 0.1–0.7%. In a survey of 47 annual medic pastures in medium and low rainfall zones of the Western Australian wheat belt in 1987, the virus was detected in leaf samples from only three sites. When inoculated mechanically, AMV systemically infected 11 cultivars and 12 selections belonging to 13 species, but did not infect one selection each of M. aculeata and M. orbicularis. Infected plants in ten species developed only faint mosaics or were symptomlessly infected, but M. littoralis, M. polymorpha and M. tornata developed distinct mottling, reduction in leaf size and, in some instances, leaf deformation and dwarfing. In pot tests, AMV infection decreased herbage and root production (dry wts) of M. polymorpha cvs Serena and Circle Valley by about 30% and 50–60% respectively, but did not decrease herbage production in M. murexcv. Zodiac. In spaced plants growing outside, AMV decreased herbage, root (dry wts) and seed production of M. polymorpha cvs Circle Valley and Santiago by about 60%.