Effect of ascochyta blight (Mycosphaerella pinodes) on yield components of single pea (Pisum sativum) plants under field conditions

Field studies were made in 1992 and 1993 to examine the yield components of pea inoculated with Mycosphaerella pinodes and those of healthy pea (sprayed with a mixture of flutriafol + chlorothalonil), in a split-plot design with the cv. Solara sown at different plant densities. Ascochyta blight was severe on leaves and on internodes of the basal part of the plants; pods had few lesions. The number and length of stems per plant were the same for diseased and healthy plants. The number of reproductive nodes and pods per stem were affected by disease only in 1993. In 1992 and 1993 respectively, disease caused reductions in the number of seeds per stem of 18% and 25%, and in seed size of 13.5% and 16.7%, compared with healthy plants. The harvest index and total biomass were lower in diseased than in healthy plants and seed yield was reduced by 40% in diseased plots. These results show a high relationship between the disease parameters (disease mean on stipules/nodes 8–18/ and on internodes/nodes 5–15/, percentages of stipules or internodes with a disease score 4, and percentage of stems encircled by lesions), plant density and yield reduction.     

Root biomechanics and whole-plant allocation patterns: responses of tomato plants to stem flexure

Cherry tomato plants (Lycopersicon esculentum Mill.) were grownwith or without stem flexure similar to that caused by windin order to determine whether stem flexure affects whole-plantbiomass allocation and increases the ability of a plant to withstandwind- induced forces. After 6 weeks of flexing (1 mm, 6 days/week),whole plants were harvested. The main differences found betweentreatments were in the primary shoot/root axis. The stem wassignificantly shorter and wider near the shoot/root junctionin flexed than control plants, both above- and below- ground.Flexed plants had significantly higher root/shoot dry weightratios than controls, but flexed plants and controls did notdiffer significantly in total leaf area, root length, or totalbiomass. Lateral roots from the top 2 cm of the taproot werenot affected by the flexing treatment for any of the factorsstudied: number of laterals, proximal diameter, elastic modulus,stress at failure, or work to failure. Lastly, the force requiredto uproot flexed plants did not differ significantly from thatfor controls. However, because their stems were shorter, flexedplants would have been subjected to smaller stem bending momentsand thus less stress near their root crowns than would controls.Moreover, flexed plants have wider stem bases, and should thusbe better able to resist the forces that affect stems. Thissuggests that in a windy situation, plants that have previouslybeen subjected to flexing could potentially withstand more forcethan unflexed controls. Key words: Anchorage, root, wind, mechanical stimulation, tomato     

Effects of inoculation with Septoria nodorum on yield components of spring wheat

Spring wheat, cv. Kolibri, was artificially inoculated with spore suspensions of Septoria nodorum, from the time of full expansion of the third leaf to the end of flowering and the effect on yield components recorded. Most components were reduced by increasing severity of infection and grain weight losses of 56 and 35% were produced on single-stemmed and tillering plants respectively, by the most severe infection. The effects on components of yield differed considerably between the main stems and the tillers and an increase in grain number on moderately infected tillers partly compensated for reductions in yield on the main stem.     

Light and Hormone Interaction in Apical Dominance in Phaseolus vulgaris L.

Gibberellic acid (GA₂), kinetin, and indole-3yl-acetic acid(IAA) each at four concentrations (0, 0.5, 5, and 50 µM)were applied alone and in all possible combinations to rootsof Phaseolus vulgaris L. grown under four different light regimes(7000, 14 000, 21 000, and 28 000 lx). GA₃ increased growthof main stem and laterals but reduced apical dominance, especiallyin the absence of, or at low kinetin concentrations. A highlevel of kinetin lowered GA₃ induced growth of main stems and,to a lesser extent, laterals. Kinetin greatly reduced apicaldominance, especially in the absence of, or at low GA₃ concentrations.IAA slightly reduced growth of main stems and laterals and slightlyincreased apical dominance. Generally the magnitude of the IAAeffects were less than those of GA₃ or kinetin and there wereless interaction between IAA and other factors than betweenGA₃ or kinetin and other factors. Light affected growth of bothmain stem and laterals but the effect was dependent on GA₃ andkinetin levels and the interactions were complex. Generallya hormone balance seems to be operative with gibberellin-promotinggrowth of main stem and laterals and cytokinins and possiblyauxins preventing excessive elongation. Differential responsesbetween main stem and lateral may be due to different localhormone concentrations and over-all responses may be temperedby light intensity.     

Modification of growth habit of Majestic potato by growth regulators applied at different times

The effect of gibberellic acid, CCC (2-chloroethyltrimethylammonium chloride) and B 9 (N-dimethylaminosuccinamic acid) was studied on growth of potato plants in pots. Growth was analysed on four occasions and changes in habit defined in terms of internode lengths, leaf areas and growth of lateral branches. Soaking seed pieces for 1 hr. in GA solution caused six internodes to elongate greatly, an effect not prevented by CCC applied when the shoot emerged from the soil. The effects on internode extension were determined by the length of the interval between GA treatment and CCC treatment. Treatment at emergence with CCC shortened all internodes and more CCC applied 4 weeks later had no effect. Late application of CCC or B9 shortened the top two lateral branches, usually very long in untreated plants. The regulators affected leaf growth differently from internode growth: usually growth regulators had less effect on leaf growth. Effects on growth depended on when the regulators were applied. Treatment with GA alone inhibited bud development at higher nodes than in untreated plants; when followed by late treatment with CCC, lateral growth at higher nodes was also less. CCC retarded development of lateral branches especially when applied early. B9 had a similar effect to CCC applied late. When regulators retarded growth of lower laterals, upper laterals often grew more than in untreated plants. Treatments did not affect the number of leaves on the main stem at first but later GA hastened senescence. GA increased the number of leaves on lateral stems, and the effect was enhanced by CCC. CCC alone increased the number of first- and second-order lateral leaves. GA lengthened and CCC shortened stolons. The effect of CCC persisted throughout the life of the plant. CCC or B 9 shortened stolons whenever applied. CCC hastened tuber initiation but slowed tuber growth. CCC at first retarded formation of lateral tubers but had no effect on the ultimate numbers of lateral and terminal tubers. The value of E (net assimilation rate) did not alter with time. CCC applied at emergence increased E, probably because it hastened tuber initiation and temporarily increased sink capacity. Although tubers formed earlier with CCC, their growth was slower and their demand for carbohydrate was also less. The increase in second-order laterals in CCC-treated plants indicates that they utilize carbohydrate that would normally go to tubers. This experiment also demonstrates that crowding leaves by shortening stems did not diminish E, possibly because another over-riding process (bigger sinks) offsets the effect of shading.     

Wheat stem sawfly‐infested plants benefit from parasitism of the herbivorous larvae

1 Parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck and their herbivorous host the wheat stem sawfly Cephus cinctus Norton, a pest of wheat Triticum aestivum, were investigated for yield in T. aestivum grown in the field. 2 Wheat stem sawfly‐infested stems had a higher yield potential than uninfested stems. However, final reproductive output was not significantly different between ears on infested stems that supported complete larval development compared with ears on uninfested stems. 3 Stems containing parasitized larvae and stems containing larvae that died before completing their development had a higher mean number of seeds and seed weight, when accounting for number of fertile spikelets of each ear, than either infested with live larvae and uninfested stems. 4 The results obtained suggest that larval feeding prevented infested stems from attaining their yield potential, and that the negative impact of the pest on wheat yield was reduced when late instar sawfly larvae were parasitized. Even though some feeding occurs before parasitism, this early damage has a comparatively low impact on yield. 5 This is the first study to show a yield benefit and enhanced plant fitness due to the wheat stem sawfly parasitoids B. cephi and B. lissogaster. This results from the maintenance of increased seed number and seed weight in the higher yielding stems that are preferentially infested by this pest.     

Incidence, symptoms, and intensity of damage by three coffee stem borers (Coleoptera: Cerambycidae) in South Yunan, China

Sampling studies were conducted in coffee plantations in South Yunan to assess the incidence, symptoms, and intensity of damage by three stem borers: Xylotrechus quadripes (Chevrolat), Acalolepta cervina (Hope), and Bacchisa sp. near pallidiventris (Thomson). Of 5,690 plants sampled in eight plantations, 440 were infested with A. cervina, 63 with X. quadripes, and three with B. pallidiventris. Plants 5-7 yr old were 10 times more heavily infested with X. quadripes than 3- to 4-yr-old plants, whereas both age groups of plants had similar levels of infestation with A. cervina. Larval galleries of the three borer species markedly differ: A. cervina and B. pallidiventris larvae develop in subcortical galleries in the main stem (A. cervina) and lateral branches (B. pallidiventris), whereas larval galleries of X. quadripes intermittently punctuate and transverse the xylem of main stems or lateral branches. Significantly more plant tissue was damaged in stems infested with X. quadripes than in those infested with A. cervina or B. pallidiventris. Stems infested with A. cervina or B. pallidiventris generally had only one or a few pupation chambers, whereas stems infested with X. quadripes contained numerous chambers. Quantitative and qualitative data collected through this study provide farmers with diagnostic tools to determine which borer species infested coffee plants. Comparison of life history traits and intensity of damage for the three borer species indicates that X. quadripes is the most severe pest of coffee in Yunan, and suggests that populations of X. quadripes have the greatest potential to steadily increase with time.     

Arabidopsis and sunflower plants with increased xylem area show enhanced seed yield

Plant architecture plasticity determines the efficiency at harvesting and plays a major role defining biomass and seed yield. We observed that several previously described transgenic genotypes exhibiting increased seed yield also show wider stems and more vascular bundles than wild‐type plants. Here, the relationship between these characteristics and seed yield was investigated. Hanging weight on the main stem of Arabidopsis plants provoked significant stem widening. Such widening was accompanied by an increase in the number of vascular bundles and about 100% of yield increase. In parallel, lignin deposition diminished. Vascular bundle formation started in the upper internode and continued downstream. AUX/LAX carriers were essential for this response. The increase of vascular bundles was reverted 3 weeks after the treatment leading to an enlarged xylem area. Aux1, lax1, and lax3 mutant plants were also able to enlarge their stems after the treatment, whereas lax2 plants did not. However, none of these mutants exhibited more vascular bundles or seed yield compared with untreated plants. Weight‐induced xylem area enhancement and increased seed yield were also observed in sunflower plants. Altogether these results showed a strong correlation between the number of vascular bundles and enhanced seed yield under a long‐day photoperiod. Furthermore, changes in the levels of auxin carriers affected both these processes in the same manner, suggesting that there may be an underlying causality.     

Interaction between Fusarium oxysporum F. vasinfectum and Cephalosporium maydis on cotton and maize

The interaction between Fusarium oxysporum (cause of cotton wilt) and Cephalosporium maydis (cause of maize late-wilt) on cotton roots is associated with an appreciable decrease in the severity of the cotton wilt disease. Reduction in infection is more pronounced when the latter fungus precedes the former in the soil than when they are inoculated simultaneously. C. maydis exerts little or no such effect when it follows F. oxysporum in the soil. C. maydis grows on the surface of cotton roots near growing points as a root-surface inhabitant. Dark red lesions are produced but these disappear, as does the fungus, when the root becomes hardened either naturally or in response to the growth of the fungus on the surface. The presence of the fungus is associated with increased production of root laterals. Cotton plants, including those which may appear healthy, show only mild internal symptoms of Fusarium infection when grown in soil inoculated with the two fungi, suggesting that the decreased severity of wilt is largely due to increased tolerance of the plants to infection with the disease as a result of increased number of root laterals. It is also possible that cotton roots with C. maydis on their surface become less suitable for the progress of F. oxysporum. F. oxysporum produces in culture a metabolite inhibitory to C. maydis. This may partly account for the little effect that the latter fungus exerts on the severity of wilt when it follows F. oxysporum in the soil. It appears that the interaction between F. oxysporum and C. maydis does not affect the pathogenicity of the latter fungus to maize.     

Interaction between Hormones, Light, and Nutrition on Extension of Lateral Buds in Phaseolus vulgaris L.

Gibberellic acid (GA₃), kinetin, and indol-3yl-acetic acid (IAA)contained in lanolin were applied in various combinations andconcentrations to decapitated stems and petioles and to budsof Phaseolus vulgaris L. GA₃ applied alone usually promotedgrowth of main stems and laterals but this was by no means consistentand occasionally it acted in the opposite way. IAA applied alonereduced lateral bud extension slightly, but not consistently;however, when applied with GA₃ or GA₃ plus kinetin, it oftenmarkedly inhibited the promotion caused by these compounds.On occasions, however, GA₃ and IAA acted synergistically topromote and sometimes to inhibit lateral shoot growth. Kinetinalone showed few significant effects on lateral shoot growthbut applied with GA₃ it often dramatically increased GA₃-inducedgrowth of main stems and laterals. The diversity of these results,which parallels that found in the literature, was shown to bepartly dependent on the point of hormone application and ageof the plant or bud, on concentration of hormone and on lightintensity or nutrition. However, no meaningful relationshipswere found and it is concluded that growth of laterals and mainstems is dependent on a hormone balance which can be criticallymodified by a wide range of internal and external factors thenature of which is still to be determined.     

Apical control of lateral bud development and shoot growth in mulberry (Morus alba)

Measurements of changes in the degree of dominance by upper laterals over lower ones in coppice shoots (1-year-old stems) of 12-year old low- pruned stumps of mulberry ( Morus alba L. cv. Shin-ichinose) were made by removal of upper stem sections (pruning) or of lateral buds (debudding.) before spring bud burst, as part of a study of the factors involved in dominance relationships between the developing buds and elongating shoots. Besides inhibition of lower laterals by the upper, leading shoots, there was evidence for mutual inhibition (competition) of neighboring laterals along the stem. Thus in stems in which every other bud, or 4 out of every 5 buds were removed, there was a delay in growth cessation of lower laterals and their greater elongation than in controls. Such competition was seen to exist even between the uppermost and sub-terminal laterals, since the former elongated more in the absence of the latter.
In contrast to high and middle pruned stems, the delay in sprouting of the buds in low-pruned stems resulted in limited elongation of the shoots from such buds. This inhibition was removed when all the stems on a stump were pruned to the same length, suggesting that it was associated with intact stems with actively growing laterals. Patterns of regrowth of the short shoots (lower laterals) after summer pruning (middle-pruned) depended on the extent of removal of other stems with vigorously growing, upper laterals. These results demonstrate that both acropetal and basipetal influences are important in bud and shoot dominance relationships.     

Interactions between Sarocladium oryzae and stem attacking fungal pathogens of rice

In laboratory tests Sarocladium oryzae, the sheath rot pathogen of rice was found to inhibit the mycelial growth of other stem-attacking rice pathogens. Among those inhibited, Sclerotium oryzae and Gaeumannomyces graminis var. graminis were most sensitive while Pyricularia oryzae and Rhizoctonia solani were less sensitive. Tissue-based tests made with rice culm segments established that Sarocladium oryzae inhibits mycelial growth and delays sclerotium formation in R. solani. Cerulenin, the toxin produced by Sarocladium oryzae showed a toxicity pattern towards rice pathogens similar to that of Sarocladium oryzae. The stem rot pathogen, Sclerotium oryzae was most sensitive to cerulenin. In two greenhouse experiments, IR58 rice plants inoculated with Sarocladium oryzae alone or together with Sclerotium oryzae, G. graminis var. graminis or R. solani were found to have reduced plant height and increased tiller number. Sheath rot severity increased when Sarocladium oryzae was inoculated as a single pathogen or together with others. Sheath rot inoculation reduced stem rot in rice plants by 76 and 58%, respectively, in Experiment 1 and 2. By its known antagonistic interaction towards stem rot and crown sheath rot pathogens which are sensitive to it and by other unknown interactions, sheath rot emerges as the dominant disease.     

Light Effects on Apical Dominance

Reducing light intensity from 18·0 klx to 5·4klx promoted main-stem growth in Phaseolus vulgaris but leftlateral extension unaffected. Shading individual laterals orapices of main stems promoted elongation of the shaded portion.Increasing day length from 8 to 16 or 24 h did not greatly affectplant growth if full-intensity and full-spectrum light was used.If, however, the additional light was supplied by incandescenttubes containing a high proportion of infra-red light, growthof main stems but not laterals was induced in proportion tothe length of the additional light period. It is suggested thatthe increased growth of the main stem in response to infra-redlight prevented the equivalent response of the laterals becauseof the enhanced ability of the main stem to suppress lateralelongation.     

Retardation of inflorescence development inCalendula officinalis by a morphactin and its application

The morphactin - chlorflurenol at 1, 5, 25, 125 and 625 μg/plant either caused total damage of the shoot apices or allowed a few inflorescences to develop with few or no flowers. The inflorescences arising in the lateral branches showed suppressed bracts and modified flowers. With time the treated plants recovered and showed a significant increase in the growth of laterals and the number of inflorescences. Thus morphactin can be used for prolonging the growth period and for obtaining more wholesome plants.     

Studies on the fungicidal control of stem lesions caused by Botrytis cinerea on glasshouse tomatoes

In glasshouse pot experiments, uptake of benomyl, thiophanate-methyl and carbendazim from equivalent soil applications (in the range 0–003– 0–035 %^a-i- ^atarateof ²&4 ml/plant) gave equal levels of control of Botrytis lesions developing from inoculations of freshly exposed leaf scars on tomato stems. Spray applications of benomyl to exposed leaf scars controlled infection at concentrations down to 0025 % a.i. The effect of lower concentrations of the stem spray could be markedly enhanced either by the addition of a mineral oil (2 % Actipron) or by a prior soil application of benomyl at a low rate which on its own had little effect on lesion development. Protectant spray applications of glycophene and vinclozolin gave levels of control quite comparable to that of benomyl at equivalent concentrations. Evidence was obtained that the lesions formed at the artificially-inoculated leaf scars at the top of the stems of young pot-grown tomato plants were larger than those lower down. In spite of this, the level of disease control with soil applications of fungicides containing or generating carbendazim (MBC) was greater at the top than at the bottom, probably because of the normal migration of the fungicides and their accumulation at the extremities of the plant. In an observation trial in a commercial crop of tomatoes, benomyl applied either as five soil drenches at approximately monthly intervals, or as two drenches followed by five sprays at three-weekly intervals, or as five sprays alone gave marked reductions in plant loss and number of Botrytis stem lesions in both cvs Eurocross BB and Cudlow Cross. Those stem lesions which did develop, however, were generally as large as those on untreated control plants. Five sprays of dichlofiuanid gave similar levels of disease control. All the treatments gave apparently higher yields (statistically untested) in Eurocross BB, but less consistent responses were recorded in Cudlow Cross.     

Dormancy and spring development of lateral buds in mulberry (Morus alba)

Patterns of spring development of lateral buds of mulberry (Morus alba L. cv. Shin-ichinose) coppice shoots on 11-year-old low-pruned stumps varied in response to girdling, pruning and arching. The erect controls showed a weak acrotonic (apex-favoring) growth habit, in which the majority of the buds, including the basal ones, sprouted and elongated in mid- and late April, and hence there was a prolonged imposition of dominance on the upper laterals in mid- and late May. In contrast, early spring girdling or pruning enhanced the activity of the upper buds of the proximal (lower) halves of the girdled stems or of the pruned stems, resulting in considerable dominance of the laterals from such buds in late April. Arching markedly inhibited buds on the under side of the arched stems, leading to poor shoots. By late April, the buds on the adaxial (upper) side readily grew into new vertical shoots, which dominated over the lateral ones. When studied by a multiple-node-cutting test, increased length of segments of post-dormant mulberry stems was accompanied by decreased bud activity of the segments and by decreased breaking ability of the lower buds within the segments, suggesting the importance of roots in the weak acrotonic habit of the erect stem in spring. By contrast, the acropetal influences of the attached stems can in part affect dominance relationships, perhaps mediated through competition for factors translocated from the roots. Continuous basal applications of abscisic acid inhibited bud break and shoot growth of the postdormant stem segments, but these inhibitory effects could be reversed by applied gibberellic acid A₃ (GA₃). Two phases of lateral bud dormancy in erect mulberry coppice shoots were identified. The first was characterized by a smaller breaking capacity in the upper buds than in the lower ones and hence by a basitonic (base-favoring) gradient in bud growth potential. The second phase corresponded to a restoration of these capabilities in the upper buds and to a change towards a linear gradient in bud growth potential, with disappearance of the dormant condition, in February and March. This gradient change during dormancy release may represent the physiological basis for the weak acrotonic habit of erect mulberry stems in spring.     

Besides stem canker severity,oilseed rape host genotype matters for the production of Leptosphaeria maculans fruit bodies

For fungal cyclic epidemics on annual crops, the pathogen carry-over is an important but poorly documented step. Plant resistance affects the pathogen development within the epidemics but we lack data on the inter-annual transmission of inoculum. For Leptosphaeria maculans on 15 oilseed rape genotypes in field during 4 growing seasons, stem canker severity was visually scored at harvest. The number of fruit bodies produced on incubated stubble was quantified using an automated image analysis framework. Our results confirm that fruit body production increases with disease severity and is significantly affected by host genotype and nitrogen supply. Tracking individual stems through incubation, we confirm for the first time that the oilseed rape genotype has a direct effect on inoculum production, not only disease severity. This major effect of genotype on inoculum carry-over should be taken into account in models of varietal deployment strategies.     

A comparison of spike and spikelet survival in mainstem and tillers of barley

Initiation and abortion of spikelet primordia on primary tillers and mainstem were compared for plants of spring barley, Maris Mink, sown on two sowing dates during 1983, in plots at the Scottish Crop Research Institute (SCRI) and at Long Ashton Research Station (LARS). Sowing date had no effect on the number of spikelets initiated on either mainstem or surviving tillers and many more spikelets were initiated on equivalent stems at LARS than at SCRI but more spikelets aborted at the former site. The final number of spikelets produced was eventually similar. Spikelet abortion was complete by anthesis and coincided with the period of rapid stem and rachis elongation and with the time over which tiller death occurred. Despite the fact that plants at SCRI produced fewer fertile tillers they outyielded those at LARS because much heavier grains were produced on the mainstem and tiller 1 of plants at the Scottish site. An interval of 2 wk between sowing had only small effects on the components of yield.     

Boron stem infusions stimulate soybean yield by increasing pods on lateral branches

Studies were carried out to determine if supplemental B (H₃BO₃) and Ca (CaCl₂) injected via a stem infusion technique into soybeans could stimulate yield by increasing pods on lateral branches, seed number, and overall seed yield. Boron treatments caused a significant 84.8% increase in the number of lateral pods/plant and a 17.6% increase in total seed weight/plant. This corresponded to a seed yield of 4170 kilograms per hectare in the B-treated plants compared to 3540 kilograms per hectare in the injected control plants, indicating that B deficiency may have been a factor in limiting yield of control plants. Ca treatments tended to accentuate the negative yield effects of apparent B deficiency.     

Host Plant Phenotype and the Impact and Development ofCarmenta mimosa,a Biological Control Agent ofMimosa pigrain Australia

The influence of host plant phenotype on the impact caused toMimosa pigraL. (Mimosaceae) plants by the feeding activity of larvae ofCarmenta mimosaEichlin and Passoa (Lepidoptera, Sesiidae) and the relationship between plant phenotype (through plant quality) and larval development were investigated under controlled conditions. Plants grown under conditions of reduced light availability were most prone to the detrimental effects of the feeding activities ofC. mimosalarvae. The relative growth rate (RGR) of most plant phenotypes could be reduced when infested withC. mimosalarvae compared to uninfested plants. Small plants infested withC. mimosaand grown under reduced light availability exhibited significant reductions in RGR sooner than large plants grown in full sun. The physical quality of stems was correlated with the severity of impact, i.e., whether stem breakage occurred. Little larval-induced mortality of plants was observed, suggesting that vascular tissues remained sufficiently intact to allow translocation. Systemic stem death arose through infection by secondary pathogens. Differences in biomass of infested versus uninfested plants of all phenotypes were associated with the loss of stems and to a lesser extent leaves. The phenotype of plants had a significant effect on the development ofC. mimosalarvae. Larvae in stems of plants with good access to reserves of soil moisture reached more advanced stages of development sooner than did those in plants which were often water stressed. This response was mediated through the combined influence of availability and nutritional quality of food. The implications of these findings to the impact of this agent in the field and the factors which may significantly influence its population dynamics are discussed.