A Comparison of the Disease Reactions of Stems and Detached Leaves of Soil and in vitro Grown Plants and Regenerants of Oilseed Rape to Leptosphaeria maculans and Protocols for Selection for Novel Disease Resistance

Protocols for selecting plant tissues of winter oilseed rape (Brassica napus subsp. oleifera) with resistance to Leptosphaeria maculans by either stem or leaf inoculation of both soil and in vitro grown plant material are described. The stem inoculation procedure gave good correlation (r = 0. 92) between the 50 day stem disease scores of eight out of nine cultivars of soil grown winter oilseed rape inoculated with isolate 41A4 of L. maculans and the N. A. B. esistance ratings or resistance data from field trials. The exception was the cultivar Liradonna. Inoculation of stems of five cultivars with isolates 41A4, 433 and 478 indicated a range of isolate virulence 478 > 41A4 > 433. This was the inverse of that observed in leaf inoculations. Application of the stem inoculation procedure to in vitro shoot cultures allowed differentiation of resistant and susceptible cultivars, including the cultivar Liradonna, after 20 days incubation at 20°C. The protocol was also applicable to plantlets regenerated from thin cell layer explants grown in vitro. Inoculations with isolate 433 allowed the differentiation of resistant, intermediately resistant and susceptible leaf material of soil grown plants, when leaf discs from young leaves were incubated on water agar supplemented with BAP (1 × 10^?5 M) at 25°C for 10 days. Intermediately resistant leaves were resistant after 10 days and susceptible after 15 days of incubation. Leaves of shoot cultures grown in vitro were more susceptible than the corresponding soil grown material. However, inoculation of old leaves with isolate 41A4 (an isolate of less virulence on leaves than 433) distinguished the cultivars after 15 days of incubation. These protocols allow the accurate assessment of resistance to L. maculans at the stem or leaf level and are of use in traditional as well as in vitro selection programmes.     

Companion planting – do aromatic plants disrupt host‐plant finding by the cabbage root fly and the onion fly more effectively than non‐aromatic plants?

Brassica and Allium host‐plants were each surrounded by four non‐host plants to determine how background plants affected host‐plant finding by the cabbage root fly (Delia radicum L.) and the onion fly [Delia antiqua (Meig.)] (Diptera: Anthomyiidae), respectively. The 24 non‐host plants tested in field‐cage experiments included garden ‘bedding’ plants, weeds, aromatic plants, companion plants, and one vegetable plant. Of the 20 non‐host plants that disrupted host‐plant finding by the cabbage root fly, fewest eggs (18% of check total) were laid on host plants surrounded by the weed Chenopodium album L., and most (64% of check total) on those surrounded by the weed Fumaria officinalis L. Of the 15 plants that disrupted host‐plant finding in the preliminary tests involving the onion fly, the most disruptive (8% of check total) was a green‐leaved variant of the bedding plant Pelargonium × hortorum L.H. Bail and the least disruptive (57% of check total) was the aromatic plant Mentha piperita × citrata (Ehrh.) Briq. Plant cultivars of Dahlia variabilis (Willd.) Desf. and Pelargonium×hortorum, selected for their reddish foliage, were less disruptive than comparable cultivars with green foliage. The only surrounding plants that did not disrupt oviposition by the cabbage root fly were the low‐growing scrambling plant Sallopia convolvulus L., the grey‐foliage plant Cineraria maritima L., and two plants, Lobularia maritima (L.) Desv. and Lobelia erinus L. which, from their profuse covering of small flowers, appeared to be white and blue, respectively. The leaf on which the fly landed had a considerable effect on subsequent behaviour. Flies that landed on a host plant searched the leaf surface in an excited manner, whereas those that landed on a non‐host plant remained more or less motionless. Before taking off again, the flies stayed 2–5 times as long on the leaf of a non‐host plant as on the leaf of a host plant. Host‐plant finding was affected by the size (weight, leaf area, height) of the surrounding non‐host plants. ‘Companion plants’ and aromatic plants were no more disruptive to either species of fly than the other plants tested. Disruption by all plants resulted from their green leaves, and not from their odours and/or tastes.     

Induction of defence-related enzymes in onion by combined application of fungal and bacterial biocontrol agents against Fusarium oxysporum f. sp. cepae

Basal rot disease of onion is a major problem in different onion growing regions of Tamil Nadu, India. Fungal and bacterial cultures were isolated and tested their efficiency against Fusarium oxysporum f. sp. cepae under in vitro conditions. Effective bacterial and fungal antagonists were tested alone and in combinations for the control of F. oxysporum f. sp. cepae in glasshouse experiments. Defence-related enzymes such as peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase were induced and accumulated in onion treated with fungal and bacterial antagonists. Defence-related enzymes were significantly higher in onion pretreated with consortial formulation of Pf12 + Pf27 + TH3 at 5 days after the challenge inoculation with F. oxysporum f. sp. cepae and gave resistance to onion against basal rot disease.     

Development of carrot inbreds with resistance to carrot fly using a single seed descent programme

Two carrot cultivars, ‘Sytan’ and ‘Long Chantenay’, representing commercially important carrot types and selected for their partial resistance to the carrot fly (Psila rosae) were crossed as the basis for a single seed descent programme. The resulting F₁ progeny were mass pollinated to produce an F₂ generation and approximately 2000 plants were raised from this segregating family in the glasshouse in 1981. By careful choice of sowing date and glasshouse temperatures it was possible to stimulate the plants to flower within 10 months. Individual king umbels were enclosed within bags and pollinated with blowflies. Resulting seed was sown in pots in the following August and the process of seed production repeated in a 12 month cycle. Each inbred line was selfed in this way over three generations until the F₅ stage. Stocks of seed were then multiplied. A total of 753 inbreds were produced by 1987. The vigour of each inbred was evaluated in glasshouse tests and the level of chlorogenic acid was determined by a fluorescence technique. The most vigorous lines with the lowest levels of chlorogenic acid were tested in field experiments against carrot fly at Wellesbourne. Nine inbreds with promising agronomic quality and moderate resistance to carrot fly were selected and seeded. These nine lines were submitted to seed companies with the aim of developing new cultivars of carrot.     

Life history parameters of <Emphasis Type="Italic">Thrips tabaci</Emphasis> (Thysanoptera: Thripidae) on six commercial cultivars of canola

The onion thrips, Thrips tabaci Lind. (Thysanoptera: Thripidae), is an important pest of the canola crop, Brassica napus L., in the Ardabil region. In this study, life history parameters of T. tabaci were investigated on six canola cultivars, namely: Talayh, Zarfam, RGS003, Opera, Option500, and Hayola401. Experiments were performed in a climate chamber set at 25 ± 1°C and 55 ± 5% RH under 16L:8D. The results indicated that the development time of immature stages was significantly longer on RGS003 than on Opera, Hyola401, Zarfam, Option500, and Talayh. The onion thrips reared on RGS003 had the lowest number of eggs laid per female (15.5) and the lowest survival rate (40%) among the tested cultivars. The lowest intrinsic rate of natural increase (r _m) and population growth rate (λ) were observed on RGS003, and were the highest on Zarfam. The generation time (T) was shortest on Zarfam (21.5 days) and longest on RGS003 (26.5 days). Similarly, the doubling time (DT) was shortest on Zarfam (4.5 days) and longest on RGS003 (8.1 days). Considering the significant effect of the host plant on the life history parameters of onion thrips, it was concluded that RGS003 is the least suitable cultivar among the other tested canola cultivars for integrated management of onion thrips in canola fields.     

Inheritance of resistance to yellow rust (Phragmidium rubi-idaei) in red raspberry

The inheritance of resistance in red raspberry (Rubus idaeus) to yellow rust (Phragmidium rubi-idaei) was studied in a diallel cross among the cultivars Boyne, Meeker, Mailing Jewel, Glen Prosen and Glen Clova. The progenies and clonally propagated parents were exposed initially in a rust-infected plantation where the incidence and severity of infection was assessed at the telial stage. The following spring leaves on new canes of the same plants were inoculated with urediniospores in a glasshouse at 18 ± 2 °C. The latent period and number of uredinia per cm² of abaxial leaf surface were determined 13 and 18 days after inoculation. Cv. Boyne developed only chlorotic flecking on inoculated leaves in the glasshouse and no sporulation was observed. It is postulated that this reaction was determined by a major gene which is designated Yr. Some of the other parents showed incomplete resistance of the slow rusting type, and segregants of Boyne selfed that were susceptible also showed low levels of rust, which suggests that Boyne carries both major- and minor-gene resistance. Diallel analyses of both the field and glasshouse data from the susceptible segregates indicated that the degree of incomplete resistance present was determined predominantly by additive gene action, though small but significant non-additive effects also occurred: cv. Meeker was the most resistant parent and contributed the most resistance to the progenies. The Meeker progenies also segregated for gene H, which determines cane hairiness and is known to be associated with resistance to other diseases. Segregants without hairs (genotypes hh) were found to be the more resistant to rust.     

Laboratory tests for leaf resistance to Botrytis squamosa in onions

Two laboratory methods of testing for resistance to Botrytis squamosa in Allium cepa, A. fistulosum and hybrid material derived from them were developed. In one method, seedlings were sprayed with conidiospores, incubated for 3 days at 15°C (2 days at 100% r.h.) and the numbers of lesions per leaf assessed. This test was destructive. The second method was non-destructive, the plants being retained for breeding purposes. Leaf segments (25 × 15 mm) or leaf discs (14 mm diameter) were inoculated individually with a drop (0·014 ml) of spore suspension, and maintained at 15°C and 100% r.h. with a 12 h photoperiod. The length of the latent period, denned as the number of days for 50% of the leaf portions to produce lesions bearing visible mycelium, was determined for each onion line in a test. The reciprocal (1/t) of the latent period was used to test for significant differences between lines by analysis of variance. With both test methods, spores were applied at concentrations that discriminated relative resistance most readily. In both seedling and leaf segment tests A. fistulosum was more resistant than A. cepa to B. squamosa. The leaf disc test indicated that cultivars of A. fistulosum differed in their resistance. In hybrid material resistance was intermediate or more like that of A. fistulosum.     

Bean seed fly (Delia platura, Delia florilega) and onion fly (Delia antiqua) incidence in England and an evaluation of chemical and biological control options

Bean seed fly and onion fly are significant pests of alliaceous crops in the UK. Their activity was monitored using yellow water traps at three field sites in England in 2002 and 2003. Bean seed fly were not split between Delia platura or Delia florilega because from the growers point of view control measures are independent of species. The traps were effective at catching bean seed fly, which was present from April until September. A total of 1729 bean seed fly were trapped in 2002 and 4501 in 2003, with peak activity in May in both years. In 2003, there appeared to be three to four peaks in abundance of the pest. Only 113 onion flies were trapped in 2002 and 23 in 2003. More male onion fly were trapped than females. Pot experiments were carried out to evaluate efficacy of a range of insecticides, garlic and two parasitic nematode species (Steinernemafeltiae and Steinernema kraussei) against bean seed fly and onion fly. Pots of salad onions were exposed to natural oviposition by bean seed fly, but the onion fly experiment was carried out in a glasshouse with eggs of the pest being inoculated into the pots. Tefluthrin seed treatment appeared to be especially effective at preventing bean seed fly damage and produced the most robust seedlings but did not appear to kill the larvae. A drench of chlorpyrifos at the ‘crook’ stage gave 100% control of bean seed fly larvae. A chlorpyrifos drench was the only treatment to give effective control of onion fly. There was some evidence that the parasitic nematode S. feltiae reduced numbers of bean seed fly larvae by about 50%. Guidelines for control of both bean seed fly and onion fly are discussed.     

Relationship between Position on the Parent Plant and Dormancy Characteristics of Seeds of Three Cultivars of Celery (Apium graveolens)

Germination and seedling emergence studies were made on seeds harvested from four different umbel positions of three cultivars of celery (Apium graveolens L.). Although heavier seeds were produced from primary umbels than from other umbels, these were less viable as measured by the germination percentage at I8°C in the light. However, germination of viable seeds from quaternary umbels was lower than that of seeds from primary umbels at 18°C in the dark when incubated with GA₄, (2 × 10 ^?4M) and seed from secondary and tertiary umbels tended to be intermediate in response. All viable seeds germinated when N⁶-benzyladenine (10^?2M) was used in combination with GA₄. Seeds from quaternary umbels of two of the cultivars had a lower high-temperature limit for germination in the dark than did seeds from other umbels. In glasshouse experiments the emergence of viable ‘quaternary’ seeds of these cultivars was higher than that of ‘primary’ seeds. Under these conditions the time to 50% of the final emergence as determined after 42 days was similar for seeds from all umbel positions within each cultivar. In two varieties seedling weights were greater from seeds of primary as compared to quaternary umbels, and in general, the largest seedlings arose from the heaviest seeds and the smallest from the lightest seeds in all three cultivars.     

The susceptibility of stems of different potato cultivars to blackleg caused by Erwinia carotovora subsp. atroseptica

The susceptibility of stems of six potato cultivars to Erwinia carotovora subsp. atroseptica was assessed in two years (1981 and 1982) either by direct inoculation in the field or by inoculation of detached stems in the laboratory. These six and a further 22 cultivars were also assessed in three years (1982-84) by inoculating stems of glasshouse-grown plants. Different methods of inoculation and types of inocula were tested. In the field, wooden toothpicks rubbed in bacterial slime were more successful in establishing infection than when dipped in a bacterial suspension, but injection of bacterial suspension with a hypodermic needle was reliable in establishing infection over a range of concentrations. Detached stems were more readily infected and gave more consistent results compared with inoculation in the field. The range of reaction of the six cultivars was similar in both detached stem and glasshouse tests. The early cultivars Pentland Javelin and Ulster Sceptre were most susceptible and of the maincrop cultivars, Maris Piper was intermediate and Desiree and King Edward least susceptible whereas Pentland Crown showed greater resistance in the glasshouse than in the field. Glasshouse tests using hypodermic inoculation indicated a range of susceptibilities; the early cultivars Manna, Maris Bard and Estima were most susceptible and the maincrop Pentland cultivars Crown, Dell, Hawk, Ivory and Squire least susceptible.     

Increasing phosphorus concentration in seed of annual pasture legume species increases herbage and seed yields

In glasshouse experiments with low levels of soil applied phosphorus (P), yields of four annual pasture legumes (Medicago polymorpha, Trifolium subterraneum, T. balansae, Ornithopus compressus) increased with increasing P concentration in the seed. In a further experiment, M. polymorpha cv. Serena was grown at the same plant density from seed of two P concentrations and two seed sizes when two levels of finely ground superphosphate were applied to the soil. Higher P concentrations in the seed increased yields of dried tops by about 30% for the first harvest (21 days), 20% for the second harvest (52 days), and 9% at maturity (103 days), and seed yields by 11%. Larger seeds increased yields of dried tops by between 6–46% for the first two harvests but at maturity yields of dried tops and seed were unaffected by seed size. None of the interactions were statistically significant (P>0.05), except for the first harvest when two interactions (P concentration in the seed × seed size (i.e. P content in seed), and P applied to the soil × P concentration in the seed × seed size) were significant at P<0.05 level. In a field experiment, Trifolium subterraneum clover seed (two cultivars) of the same size but with two different P concentrations was sown at the same plant density and two levels of granulated (0.2–5 mm) superphosphate were applied to the soil surface. The higher level of superphosphate increased dried herbage yields of the dense clover swards by three- to four-fold 90 and 120 days after sowing. The higher P concentration in the seed increased yields of dried herbage by between 50 to 25%, depending on the level of P applied to the soil and the harvest date.     

Effect of host plant on susceptibility of whitefly Bemisia tabaci (Homoptera: Aleyrodidae) to the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales)

We determined host plant effect on susceptibility of whitefly Bemisia tabaci to the entomopathogenic fungus Beauveria bassiana under controlled conditions. Insects were reared on cucumber, eggplant, tomato or cabbage. Fungal suspensions of 1×10⁴, 10⁵, 10⁶, 10⁷ and 10⁸ conidia/mL were applied on second-instar nymphs. Nymphal survival significantly differed among different host plant species on which the nymphs were reared. Ten days after inoculation with 1×10⁸ conidia/mL, percent survival was 4.2±0.7, 9.6±0.4, 13.4±0.8, and 24.3±0.9% on cucumber, eggplant, tomato and cabbage, respectively. Average survival times of nymphs were also significantly influenced by host plant species. After inoculation with 1×10⁸ conidia/mL, survival times were 4.8±0.15, 6.0±0.11, 5.7±0.13, and 6.2±0.08 days for nymphs reared on cucumber, eggplant, tomato, and cabbage, respectively. Virulence also differed depending on host plant species; 10 days after inoculation, LC₅₀ values were 4.6×10⁴, 1.6×10⁵, 4.2×10⁵ and 2.1×10⁶ conidia/mL on cucumber, eggplant, tomato and cabbage, respectively. Nymphs on cucumber showed highest susceptibility.     

The effect of VA mycorrhizal fungi,phosphorus and drought stress on the growth of Acacia nilotica and Leucaena leucocephala seedlings

The effect of vesicular-arbuscular mycorrhizal (VAM) fungi on growth and drought resistance of Acacia nilotica and Leucaena leucocephala seedlings was studied in a glasshouse experiment. The experimental design was a 2·2·2 factorial: ± mycorrhizal inoculation, ± application of phosphorus fertilizer and ± repeated drought treatment. The growth promoting effect of VAM fungi equalled the effect of phosphorus fertilization after 12 weeks. The drought treatment reduced seedling biomass and nodulation. Differences between the plant species were found with respect to growth improvements due to VAM inoculation and/or phosphorus fertilization under drought stress conditions. The results are discussed in relation to plant drought resistance and reforestation in the subhumid to arid tropics.     

Genetic analysis of resistance in Brussels sprout to cauliflower mosaic and turnip mosaic viruses

A total of 28 inbred lines of Brussels sprout were assessed in the glasshouse for their reaction to inoculation with cauliflower mosaic (CaMV) or turnip mosaic (TuMV) virus. There was significant variation for resistance to both viruses. From the 28 inbred lines parents were chosen for two 9 × 9 diallel crossing programmes. The parents and their F₁ progeny were assessed for their reaction to CaMV or TuMV in the field. There was significant additive and non-additive (dominance) variation but no maternal effects. Resistance to both viruses was generally dominant but with some evidence of a recessive gene for resistance to CaMV. Resistance to TuMV and CaMV was apparently controlled by at least four genes and two genes respectively. The heritability of resistance to each virus was high. The implications for breeding F₁ hybrid Brussels sprout cultivars are discussed.     

The Effect of Environmental Conditions on the Expression of Disease in Cultured Tissues of Brassica napus ssp. oldfera Infected with Leptosphaeria maculans

As a basis for devising an in vitro screening programme, culture conditions were optimized so that tissue cultures from two resistant cultivars of Brassica napus ssp. oleifera (Mikado, Bienvenu) and two susceptible cultivars (Lesira, Ceres) could be differentiated using a disease scoring scheme, when inoculated with Leptosphaeria maculans. Tissues inoculated included thin cell layer explants from soil-grown plants and in vitro-grown shoot cultures and callus tissue formed on such explants. The period of incubation and the incubation temperature were of importance in the development of differential disease reactions. Increasing temperature generally resulted in an increase in infection and too great an incubation period resulted in total overgrowth of the tissue. Increasing concentrations (1 × 10^?6 M-1 ×10^?4 M) of the auxins 1-naphthylacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D) and mdole-3-acetic acid (IAA) in the culture medium, resulted in a decrease in disease score of the thin cell layer (TCL) explants from soil-grown plants. The cytokinins examined 6-benzyl-aminopurine (BAP) and 6-4-hydroxy-3-methyl-2-enylaminopurine (zeatin), reduced the extent of infection of the TCL explants when used in combination with the auxin NAA. Medium containing NAA at a concentration of 1 × 10^?6 M in combination with BAP at a concentration of 1× 10^?6 or 1 × 10^?4 M allowed differentiation of the disease reactions of the resistant and susceptible cultivars, when the explants were incubated for 10 days at 20 °C after inoculation. Similar conditions of incubation and the addition of NAA (1 × 10^?6 M) combined with BAP (1 × 10^?6 M) to the medium also allowed the differentiation of the disease reactions on TCL explants from stems of in vitro shoot cultures of the cultivars Mikado and Lesira. Increasing concentrations of the auxin NAA and the cytokinin BAP resulted in a reduction in the mean disease score of the callus tissue produced on TCL explants from soil-grown plants, and NAA (1 × 10^?5 M) combined with BAP (1 × 10^?6 or 1 × 10^?5 M) allowed differentiation of resistance and susceptibility in callus tissues when incubated for 5 days at 20 °C. 2,4-D did not allow differentiation of the cultivars. This was in contrast to the inoculation of callus tissue attached to TCL explants of in vitro shoot cultures, where combinations of 2,4-D and BAP at concentrations of 1 × 10^?6 M allowed differentiation of the resistant and susceptible cultivars. These findings provide a basis for designing selection protocols of value in both traditional as well as in vitro breeding programmes to select lines of oilseed rape with resistance/novel resistance to L. maculans.     

Screening of cassava varieties for resistance to root-knot nematodes

Twenty cassava cultivars were screened in micro-plot experiments in the green house of Institute of Agricultural Research and Training, Obafemi Awolowo University, Moor Plantation, Ibadan for root-knot nematode resistance. Four weeks after planting, each plant was inoculated with 5000 eggs of Meloidogyne incognita. There were three replications per cultivar. The plants were uprooted and assessed for resistance after 60 days of inoculation. Assessment of plant damaged was determined by gall index and reproductive factor. Based on host status rating, 3 cultivars were found to be resistant, 4 cultivars were tolerant, 10 cultivars ere susceptible while .3 cultivars were hypersusceptible. All the screened cultivars are resistant to cassava mosaic disease and other major pests of cassava like bacterial disease, anthracnose disease, cassava green mite and cassava mealy bug. They are all high yielding, suitable for food, industry and livestock feed.     

Genetic analysis of the interaction between <Emphasis Type="Italic">Allium</Emphasis> species and arbuscular mycorrhizal fungi

The response of Allium cepa, A. roylei, A. fistulosum, and the hybrid A. fistulosum × A. roylei to the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied. The genetic basis for response to AMF was analyzed in a tri-hybrid A. cepa × (A. roylei × A. fistulosum) population. Plant response to mycorrhizal symbiosis was expressed as relative mycorrhizal responsiveness (R′) and absolute responsiveness (R). In addition, the average performance (AP) of genotypes under mycorrhizal and non-mycorrhizal conditions was determined. Experiments were executed in 2 years, and comprised clonally propagated plants of each genotype grown in sterile soil, inoculated with G. intraradices or non-inoculated. Results were significantly correlated between both years. Biomass of non-mycorrhizal and mycorrhizal plants was significantly positively correlated. R′ was negatively correlated with biomass of non-mycorrhizal plants and hence unsuitable as a breeding criterion. R and AP were positively correlated with biomass of mycorrhizal and non-mycorrhizal plants. QTLs contributing to mycorrhizal response were located on a linkage map of the A. roylei × A. fistulosum parental genotype. Two QTLs from A. roylei were detected on chromosomes 2 and 3 for R, AP, and biomass of mycorrhizal plants. A QTL from A. fistulosum was detected on linkage group 9 for AP (but not R), biomass of mycorrhizal and non-mycorrhizal plants, and the number of stem-borne roots. Co-segregating QTLs for plant biomass, R and AP indicate that selection for plant biomass also selects for enhanced R and AP. Moreover, our findings suggest that modern onion breeding did not select against the response to AMF, as was suggested before for other cultivated species. Positive correlation between high number of roots, biomass and large response to AMF in close relatives of onion opens prospects to combine these traits for the development of more robust onion cultivars.     

Reaction of some tomato cultivars to tomato leaf curl virus and evaluation of the endophytic colonisation with Beauveria bassiana on the disease incidence and its vector,Bemisia tabaci

Tomato line LA1478 and Pusa Ruby were resistant to tomato leaf curl virus (TLCV) disease. They registered higher plant height, number of branches, total phenol content and yield per plant than the other cultivars. Variety Peto 86 was tolerant to the disease while the other popular tomato cultivars, i.e. Ace, Early Pack, Money Maker, Prichard and Strain B were highly susceptible to the disease. Plant height and number of branches per plant revealed significantly positive association with fruit yield per plant. The disease index of TLCV exhibited significant negative correlations with plant height, total phenol content and fruit yield per plant – 0–4 and 5–25 adult whiteflies were observed on resistant susceptible cultivars. In the case of epiphytically colonisation by Beauveria bassiana conidia, not all developing hyphae on the leaf surface penetrated the whitefly cuticle. Many of the germ tubes elongated to a short distance before terminating its growth. On the other hand, the rapid staining of tomato tissues injected with B. bassiana conidial suspension indicates that the entomopathogenic fungus was established inside tomato tissues until the end time of the trial. The direct injection with the spore suspension yielded high post-colonisation, where the fungus was recovered from sites distant from the point of inoculation. This indicates that the fungus has the potential to move throughout the plant tissues. Laboratory bioassay of tomato whitefly feeding on tomato tissues containing B. bassiana conidial spores indicates that plant endophytic colonisation with entomopathogenic fungi may reduce insect survival on these plants. LT₅₀ values of the test diet were between three and four days. The mortality of Bemisia tabaci was high in the case of endophytically colonisation compared to epiphytically one (90.0% compared to 10.0% during three days) for whiteflies fed tomato tissues containing 1.5 × 10⁷ B. bassiana spores/ml. Application of B. bassiana as an artificial endophyte inside tomato plants can be an important component in the integrated control of tomato whiteflies. The endophytic colonising can achieve biocontrol effect based on induced disease resistance in plant tissues. According the available references, this is the first report on B. tabaci controlling by plant endophytic treatment.     

The effect of Solanum tuberosum×S. vernei hybrids on hatching of the potato cyst nematode Globodera pallida

The hatching activity of partially resistant Solanum tuberosum×S. vernei clones and susceptible cultivars was investigated in a series of tests with G. pallida conducted in pots in the glasshouse. Differences in hatching were apparent, with the partially resistant clones generally stimulating a lower total hatch than the S. tuberosum cultivars. It is concluded that reduced hatching activity can make a small contribution to overall resistance and perhaps also to the tolerance of a clone to G. pallida.     

Genotypic responses of scab-resistant apple cultivars/selections to two strains of Erwinia amylovora and the inheritance of resistance to fire blight

Apple cultivars and selections were tested for resistance to two strains of Erwinia amylovora following shoot tip inoculation in the greenhouse. Cv. Liberty was resistant to strain Ea 273, and Priscilla, Delicious and Coop 17 were highly resistant to strain Apple # 1. A significant genotype x strain interaction was obtained suggesting a differential host × pathogen interaction. Segregation of seedlings derived from 16 controlled crosses after fire blight inoculation indicated that resistance to fire blight is quantitatively controlled with evidence for presence of dominant additive gene effects.