Screening wild Lycopersicon species for resistance to powdery mildew (Oidium lycoperiscum)

Since the late 1980s powdery mildew, designated Oidium lycopersicum, frequently invaded the tomato crop in Western Europe. All commercial cultivars are susceptible. To screen for resistance in wild species a reliable and efficient disease test was developed. Young plants with two to three true leaves are inoculated at high relative humidity by spraying with a freshly prepared suspension of 2×10⁴ conidia, ml^–1. Symptoms are periodically evaluated according to a scale based on the percentage of leaf area with mycelium.One hundred and twenty seven accessions, representing eight wild Lycopersicon species, were screened for resistance to O. lycopersicum. A large variation in resistance was found between species. L. hirsutum was the most resistant species; L. pennellii was moderately resistant; species of the subgeneric group of L. esculentum and of the peruvianum-complex were all susceptible. L. parviflorum was classified separately due to a large variation between accessions. Except for this species, a low variation was found between accessions within species. High levels of resistance were observed in four accessions of L. hirsutum, in one of L. parviflorum and in one of L. peruvianum. This resistance is characterized by a very low disease incidence and a strongly restricted mycelium growth and lack of sporulation.     

Inheritance of foliar zingiberene contents and their relationship to trichome densities and whitefly resistance in tomatoes

The sesquiterpene zingiberene, present in leaf glandular trichomes, is reportedly responsible for the high level of arthropod resistance found in Lycopersicon hirsutum var. hirsutum. This paper reports on the inheritance of zingiberene contents and of the various types of glandular trichomes in the interspecific cross L. esculentum × Lycopersicon hirsutum var. hirsutum. Plants of L. esculentum ‘TOM-556’ (= P₁), L. hirsutum var. hirsutum ‘PI-127826’(= P₂), F₁ (P₁ × P₂) and F₂ (P₁ ×P₂) were evaluated for zingiberene contents and densitities of and glandular (types I, IV, VI and VII) trichomes. Broad sense heritabilities were high for all traits studied (0.678, 0.831, 0.996, 0.799 and 0.717 respectively for zingiberene and trichome types I, IV, VI, VII). There were significant positive genetic correlations between zingiberene contents and densities of trichomes types IV, VI and VII. Inheritance of zingiberenecontents can be explained mostly by the action of a single major locus, inwhich the allele from L. hirsutum that conditions high content is incompletely recessive over the allele from L. esculentum. Action of an incompleteley recessive allele in one major locus appears to be evident for densities of trichome types IV, VI and VII, but there is also evidence of the action of other epistatic loci for types IV and VI. F₂ genotypes selected for high zingiberene levels showed higher levels of resistance to the silverleaf whitefly Bemisia argentifolii than L. esculentum ‘TOM-556’, levels that were comparable those found in L. hirsutum var. hirsutum ‘PI-127826’ and other whitefly resistant accessions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Zingiberene-mediated resistance to the South American tomato pinworm derived from Lycopersicon hirsutum var. hirsutum

The Lycopersicon hirsutum var. hirsutum accession PI 127826 is recognized as a good source of resistance to arthropod pests due to the action of the allelochemical zimgiberene, a sesquiterpene present in its glandular trichomes. Five genotypes were selected from the F₂ generation of the interspecific cross Lycopersicon esculentum ‘TOM-556’ × Lycopersicon hirsutum var. hirsutum ‘PI 127826’, based on their low levels (BPX-368-clone#56) or high levels(BPX-368-clone#92, BPX-368-clone#105,BPX-368-clone#179, BPX-368-clone#250) of zingiberene. The five F₂ genotypes were tested for resistance to the South American tomato pinworm Tuta absolutaalong with accession L. esculentum ‘TOM-556’ (pinworm susceptible), and the accessions L. hirsutum var. hirsutum ‘PI 127826’ and L. pennellii ‘LA716’ (resistant). The F₂ clones selected for high foliar zingiberene levels showed lower scores for leaflet lesion type(LLT), percent leaflets attacked (PLA) and overall plant damage (OPD) than the low zingiberene genotypes. The results indicated that zingiberene mediates resistance to the South American pinworm, based on feeding and on ovipositing deterrence, in populations derived from the interspecific cross between Lycopersicon. esculentum and Lycopersicon hirsutum var. hirsutum. Indirect selection for high foliar zingiberene content is suggested as an efficient technique for breeding tomatoes for resistance to the South American tomato pinworm. This revised version was published online in July 2006 with corrections to the Cover Date.     

Field and greenhouse evaluation of the components of partial resistance to early leafspot in peanut

Summary Ten peanut (Arachis hypogaea L.) genotypes were evaluated fro components of partial resistance to Cercospora arachidicola Hori in the field and in two detached leaf tests in the greenhouse. The relationships among the resistance components in the two environments were examined by computing rank correlations among the components measured in the greenhouse and among those measured in the field. A comparison of field and greenhouse testing for partial resistance was made by determining the correlations between components measured in the two testing methods. The genotypes were significantly different for all the components of resistant measured in the field and for most of the components measured in the greenhouse. In the field study necrotic area/10 cm² leaf area was moderately correlated (r=0.58) with lesion number/10 cm² leaf area and highly correlated (r=0.71–0.76) with total lesion number, predicted number of days after planting (X) to reach a standard lesion count, and defoliation. In the greenhouse only the correlation between necrotic area (mm²)/10 cm² leaf area and sporulation/leaf was highly significant (r=0.71–0.83) in both greenhouse tests. Necrotic area (mm²)/10 cm² leaf area measured in the field was significantly correlated with that measured in the greenhouse (r=0.66). Sporulation/leaf measured in the greennhouse was significantly correlated (r=0.66) with lesion increase in the field (measured as predicted X). It should thus be possible to evaluate and select for components of partial resistance in the greenhouse to develop resistant lines for the field.     

Resistance in Lycopersicon hirsutum f. glabratum to the greenhouse whitefly (Trialeurodes vaporariorum) increases with plant age

Summary In this study genetic variation for resistance to the greenhouse whitefly (Trialeurodes vaporariorum) of four genotypes of tomato (L. esculentum) and two subspecies of L. hirsutum was investigated. Resistance was quantified by the whitefly life history components adult survival, oviposition rate, pre-adult survival and developmental period, measured on plants inoculated with whiteflies in clip-on cages.The largest differences between species were found when life history components were measured on adult plants of about four months old. On L. hirsutum f. glabratum whiteflies had the lowest adult survival, oviposition rate and pre-adult survival. On L. hirsutum these components were intermediate whereas on all L. esculentum genotypes they were highest. The variation between plants was low compared to the variation within plants. These results indicate that single plant tests can be used to determine accurately genetic variation between individual plants in a segregating population.     

Low temperature seed germination of Lycopersicon species evaluated by survival analysis

Summary Low temperature germination responses were evaluated for 18 high altitude accessions representing five wild Lycopersicon species and 19 accessions of L. esculentum which have reputed ability to germinate in the cold. Survival analysis indicated that one accession of L. chilense germinates better at 10°C than PI 120256, the fastest-germinating L. esculentum genotype, and that PI 120256 germinates as well as PI 126435 (L. peruvianum). Additional wild ecotypes exhibiting rapid germination at 10°C were identified from L. peruvianum and L. hirsutum. These ecotypes may possess genetic potential for introgressing cold germination ability into L. esculentum cultivars.     

New sources of major gene resistance in Lactuca to Bremia lactucae

Summary A total of 1789 accessions of several lettuce collections was screened to find new major gene resistance to the downy mildew fungus Bremia lactucae Regel. The accessions belonged to the species Lactuca sativa (N=1288), L. serriola (N=399), L. saligna (N=52) and L. virosa (N=50). A total of 20 races of B. lactucae were used, 14 of which were NL-races, isolated from cultivated lettuce in the Netherlands. The other six races were isolated from wild L. serriola in Czechoslovakia. The accessions were initially screened with two races: NL1 and NL3. Accessions with resistance to one or both of these races were tested with the other races. Phenotypes with new resistance were found in accessions of all four Lactuca species. Of L. sativa, four accessions were found with resistance phenotypes that could not be explained by combinations of known major genes. Many accessions of L. serriola had resistance phenotypes that indicated the presence of unknown resistance genes. All interactions between accessions of L. saligna and races of B. lactucae were incompatible in leaf disc tests, except for four accessions, which showed some sporulation with race NL6. Several accessions of L. virosa were resistant to all races used. Other accessions of L. virosa gave a race-specific interaction with B. lactucae.     

Evaluation of slow rusting resistance components to leaf rust in CIMMYT durum wheats

Information about slow rusting resistance to leaf rust (Puccinia triticina) in durum wheat (Triticum turgidum var. durum) is limited. Three slow rusting components, latent period, receptivity, and uredinium size, were determined at the adult plant stage for seven durums with slow rusting resistance to leaf rust and two susceptible durums in three greenhouse experiments. Additionally, area under the disease progress curve (AUDPC) and final disease severity (FDS) were determined in three field trials under artificial epidemics with the same P. triticina race BBG/BN. Compared to the most susceptible check, the AUDPC and FDS of slow rusting resistant durums were significantly lower and ranged from 13–47 to 22–59%, respectively. The latent period was significantly longer (8.5–10.3 days) and uredinium size significantly smaller (8.1–14.8 × 10⁻² mm²) on slow rusting durums than on the susceptible checks (8.0 days and 17.3–23.8 × 10⁻² mm², respectively). Uredinium size was the most stable slow rusting component across experiments. Correlations between uredinium size versus AUDPC and uredinium size versus FDS for each environment were high (r = 0.86–0.88). Correlations between latent period and field parameters were significant (r = −0.60 to −0.80). Correlations between receptivity and the field parameters were not significant. A multiple regression analysis showed that the variation in AUDPC and FDS was significantly explained only by uredinium size (P < 0.0001). The best slow rusting resistant lines can be used for developing high-yielding durums with more durable resistance to leaf rust.     

Characterization of the resistance to <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in local potato cultivars in Bolivia

This experiment was carried out to investigate whether and how much field resistance to late blight, caused by Phytophthora infestans, is present in the local cultivated potato germplasm. In total 36 entries were compared in a field experiment in an area highly conducive to late blight development. Of the 36 cultivars 32 were local cultivars belonging to five Solanum species, S. tuberosum (1 accession), S. andigena (18), S. juzepczukii (2), S. stenotomum (9) and S. ajanhuiri (2). The other four cultivars were derived from breeding programmes, one being the Dutch cultivar Alpha used as a highly susceptible control. The 36 cultivars were planted according to a simple 6 × 6 lattice design with three replicates. Each replicate was divided in six incomplete blocks each with six cultivars. The disease severity was assessed weekly during 9 weeks starting 48 days after planting. The area under the disease progress curve (AUDPC) was used as a measure of the field resistance. Nine isolates from surrounding potato fields were tested for their virulence to the resistance genes R1–R11 using 22 differential cultivars. The components of the field resistance of 19 of these cultivars were compared in the greenhouse using a local isolate with virulence to all known R-genes, except to R9. The nine isolates represented seven races with a race complexity varying from 7 to 10 virulence factors. All isolates carried virulence against R1, R2, R3, R7, R10 and R11, while virulence against R9 was absent. The AUDPC among the 32 local cultivars ranged from very large, significantly larger than that of ‘Alpha’ to very small. The AUDPC from S. stenotomum accessions ranged from very large to intermediate, those from S. andigena accessions from large to very small. Especially among the S. andigena accessions interesting levels of field resistance were found. Four components of field resistance were assessed, latency period (LP), lesion size (LS), lesion growth rate (LGR) and relative sporulation area (RSA). All four showed a considerable variation among the cultivars. The LP ranged from 3½ to 6 days. The LS ranged from 225 mm² to 20 mm². The LGR varied about six-fold, the RSA more than 10-fold. The components tended to vary in association with one another. LP and LGR were well associated with each other and had a significant correlation with the AUDPC.     

Relationships between trichome types and spider mite (Tetranychus evansi) repellence in tomatoes with respect to foliar zingiberene contents

Zingiberene, a sesquiterpene present in glandular trichomes of Lycopersicon hirsutum Dunal var. hirsutum ‘PI-127826’, is responsible for the high level of arthropod resistance in this taxon. The current paper has the following objectives: (a) to quantify zingiberene content in tomato plants obtained from the interspecific cross L. esculentum Mill. × L. hirsutum var hirsutum; (b) to identify, classify and quantify glandular and non-glandular trichome types present in those plants; (c) to assess the level of resistance of those genotypes to spider mites (Tetranychus evansi); (d) to estimate correlations between glandular trichomes, zingiberene contents and mite repellence. Zingiberene content were quantified by a colorimetric method (Freitas, 1999); trichomes were counted from foliar paradermic slide preparations; mite resistance was assessed by a repellence test (Weston & Snyder, 1990). The results indicate that indirect selection for zingiberene content led to correlated increases both in the number of glandular trichomes (particulary type IV) and in the levels of mite repellence. These results were found both in BPX-368 [=F2 (L. esculentum ‘TOM-556’ × L hirsutum var. hirsutum ‘PI-127826’)] and in the subsequent generation BPX-368B (which represents one additional backcross to L.esculentum). Zingiberene appears therefore to be the main factor involved in mite repellence. Density of glandular trichomes in tomato leaflets markedly influences total zingiberene content. Type IV trichome density was the highest, and it was highly correlated to zingiberene content. Graduate Student; This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-temperature-related growth and photosynthetic performance of alloplasmic tomato (Lycopersicon esculentum Mill.) with chloroplasts from L. hirsutum Humb. & Bonpl.

Growth and photosynthetic performance were analyzed in alloplasmic tomato at a high- (25/17 ^°C; HTR) and low-temperature regime (12/6 ^°C; LTR) in order to establish the role of cytoplasmic variation on low-temperature tolerance of tomato (Lycopersicon esculentum Mill.). Four alloplasmic tomato lines, containing the nuclear genome of tomato and the plastome of L. hirsutum LA 1777 Humb. & Bonpl., an accession collected at high-altitude in Peru, were reciprocally crossed with 11 tomato entries with a high inbreeding level and a wide genetic variation, resulting in a set of 44 reciprocal crosses. Irrespective of growth temperature, alloplasmic families with alien chloroplasts of L. hirsutum (h) were on average characterized by a high shoot biomass, a large leaf area, and a low specific leaf area in comparison with their euplasmic counterparts. These results do not directly point to an advantageous effect of h-chloroplasts on biomass accumulation at low temperature but rather towards a small general beneficial effect on growth and/or distribution of assimilates. Significant chloroplast-related differences in photosynthetic performance, however, were not detected at both temperature regimes, indicating that h-chloroplasts can properly function in a variable nuclear background of L. esculentum. It is concluded that chloroplast substitution is not an effective method for breeding tomato plants with improved low-temperature tolerance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to Didymella lycopersici Klebb. in tomato (Lycopersicon Mill.)

Summary The inheritance of the resistance to Didymella lycopersici was studied on F₃- and Bc₁-lines from interspecific crosses of L. esculentum with L. hirsutum and with L. hirsutum glabratum. The resistance is not monogenic and is inherited in dominant fashion. The high h² values based on line means offer possibilities to seleet efficiently for enhanced levels of resistance.     

Evaluation of a collection of faba bean (Vicia faba L.) genotypes originating from the Maghreb for resistance to chocolate spot (Botrytis fabae) by assessment in the field and laboratory

Screening of 136 faba bean lines forresistance to chocolate spot caused by thefungus Botrytis fabae was conductedin field conditions with artificialinoculation. Detached leaves of thesegenotypes were also assessed for diseaseseverity after inoculation under controlledconditions with a B. fabaesuspension. The BPL710 and Aguadulcegenotypes were inserted as resistant andsusceptible checks, respectively. Diseasesymptoms were scored visually in bothexperiments. Diameter of lesions andproduction of spores were measured in thedetached leaf assay. The disease scoreindex and diameter of lesions were used tocalculate the area under the diseaseprogress curve (AUDPC) to measure thedisease progress. Significant differenceswere detected among genotypes for reactionto the disease in the field. However, nocomplete resistance was observed. Forhighly susceptible and highly resistantgenotypes, the laboratory assay generallyled to the same result as the field test,nevertheless, for more intermediate levelsthe agreement was weak. On detached leaves,diameter of lesions was significantlycorrelated to the AUDPC of disease scores(r = 0.89) and moderately correlated tosporulation (r = 0.52). The correlationbetween field AUDPC and detached leaf AUDPCof disease scores was low (r = 0.26). A lowcorrelation was also observed between fieldAUDPC and lesion size (r = 0.30) andbetween field AUDPC and sporulation (r =0.32). Among the 136 genotypes evaluated inthis study, nine were convincingly andhighly resistant in both tests. FRYM167 andFRYA58 genotypes were the most resistantwith low AUDPC of disease scores, low AUDPCof lesion diameter and low sporeproduction. These genotypes obviously havepartial resistance.     

Variation in partial resistance to barley leaf rust (Puccinia hordei) and agronomic characters of Ethiopian landrace lines

An inventory of 481 lines derived from 12 Ethiopian barley (Hordeum vulgare L.) landraces and the checks was made for partial resistance to Puccinia hordei under greenhouse and field conditions at Adet, Ambo and Sinana Agricultural Research Centers in 2003 and 2004 cropping seasons in Ethiopia. The experiments were laid out in a triple lattice design. Each plot consisted of two rows of 1–m long with spacing of 0.20 m between rows. The overall mean leaf rust epidemics varied from area under disease progress curve (AUDPC) of 86 to 1,835. The disease was as high as AUDPC 1,378 on the susceptible check L94. Highly significant variations were recorded between and within the landraces/lines in leaf rust incidence, severity, days to heading, plant height, thousand seed weight and yield. Similarly, the variations between and within barley groups from three altitude areas and three ear-types were significant. Landraces 1686, 3255, 3262 and 3783 had the least and landraces 219900, 3975 and 3980 had the highest leaf rust severity. Of the 481 lines tested, 413 (86%) had significantly lower disease than the susceptible check, but not than the partial resistant check Vada. In contrast, the yields were more for lines with less disease than for those with high. The frequency of resistant landraces/lines was more in altitude 2,301–2,500 m, and irregular and two rows ear-types than in lower altitude areas and six rows ear-type. Nevertheless, the correlation and regression analysis revealed the adverse effect of the disease in the yields of barley. The 413 lines with high infection types at seedling stage and lower AUDPC under field conditions possess partial resistance to leaf rust.     

Trichomes on leaves of Lycopersicon hirsutum,L. esculentum and their hybrids

Summary Density of certain types of trichomes were characterized on leaflets of Lycopersicon hirsutum, L. esculentum and their hybrids. Trichome density covaried with leaflet development, and depending on the species and type of trichome, density also covaried with leaflet surface. Type IV trichomes were not observed on leaflets of L. esculentum and Type V trichomes were not observed on leaflets of L. hirsutum. Type IV and V trichomes were present on F₁ hybrids and densities of these two types of trichomes segregated in the F₂ population. When corrected for differences of leaflet size between L. hirsutum and L. esculentum, densities of Type VI trichomes were more similar between species than uncorrected densities. There was little difference in Type VI density among F₂ individuals. The appearance, lipid and phenol staining properties, and native fluorescence of the multicellular tip of the Type VI trichome differed between L. hirsutum and L. esculentum. F₁ hybrids were intermediate for these characters and these characters segregated in the F₂ generation.The investigation reported in the paper (84-10-94) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This material is based upon work supported, in part, by the U.S. Department of Agriculture, Agreement No. 59-2213-1-1-717-0 (Competitive Research Grants Program).     

Combining ability analysis of Fusarium head blight resistance in western European wheat lines

The inheritance of Fusarium head blight (FHB) resistance was investigated in eight western European wheat lines using a half-diallel of F₁ crosses. The parents and F₁ crosses were point-inoculated, with a highly aggressive isolate of Fusarium graminearum, in replicated field and glasshouse trials. Type II resistance was assessed by measuring the % FHB spread and % wilted tips. There was a good correlation between the two disease parameters, % FHB spread area under the disease progress curve (AUDPC) and % wilted tips AUDPC (r = 0.86, P < 0.01). Correlation coefficients between the field and glasshouse environments were r = 0.46 (P < 0.01) for % FHB spread AUDPC and r = 0.40 (P < 0.05) for % wilted tips AUDPC. Both general combining ability (GCA) and specific combining ability (SCA) effects influenced the inheritance of FHB resistance, suggesting that in this set of parents both additive and non-additive (dominance or epistatic) effects influence the inheritance of type II FHB resistance. Highly significant GCA-by-environment (P < 0.0001) and SCA-by-environment (P < 0.005) interactions were also observed. Specific combinations of western European wheat varieties were identified with type II FHB resistance at a level equal to or more resistant than the winter wheat variety ‘Arina’.     

Heritability estimates of spot blotch resistance and its association with other traits in spring wheat crosses

Summary Spot blotch caused by Cochliobolus sativusis considered a major disease problem of wheat(Triticum aestivumL.) in the warm areas of South Asia. This study estimated heritability (h ²) of resistance to spot blotch and its correlation with days to heading DH) and maturity (DM), one-hundred-kernel weight (HKW), and plant height (PHT) in 14 crosses involving four resistant (‘Attila’, ‘Chirya 7’, ‘G 162’, and ‘SW89.5422’) and two susceptible (‘Sonalika’ and ‘HD2329’) wheat genotypes. Data were recorded on F₅and F₆lines in fields under natural epidemics of spot blotch in 2003 and 2004, respectively. Heritability was estimated for area under disease progress curve (AUDPC), AUDPC/day, and the highest disease score (HDS) using offspring-parent regression (h _op ²) and realized heritability (h ² _R) procedures. Heritability estimates were low to high in terms of AUDPC (0.21 < h _op ²< 0.64; 0.32 < h _R ²< 0.70), AUDPC/day (0.40 < h _op ²< 0.96; 0.42 < h _R ²< 0.99), and HDS (0.29 < h _op ²< 0.92; 0.32 < h _R ²< 0.95). The h ²estimates for AUDPC/day were higher than for AUDPC and HDS. Estimates of h _R ²were by and large higher than h _op ²in the same cross. A weak negative or nonsignificant correlation of spot blotch score with HKW, DH, DM, and PHT indicated that independent selection for resistance and these agronomic traits is possible.     

Assessment of Gossypium sturtianum and G. australe as potential sources of Fusarium wilt resistance to cotton

When challenged with Fusarium oxysporum f. sp. vasinfectum (Fov) from vegetative compatibility groups (VCGs) 01111 and 01112 in glasshouse tests, Gossypium australe Mueller and Gossypium sturtianum Willis accessions showed a variety of disease responses ranging from highly resistant to highly susceptible. Under high disease pressure G. sturtianum accession Gos-5275 was significantly more resistant than the commercial G. hirsutum cultivars that are designated standards for Fusarium resistance by Australian cotton breeders. Under low disease pressure G. sturtianum accession Gos-5250 was more susceptible than a highly susceptible commercial cultivar. A series of glasshouse tests was performed at two locations (Indooroopilly, QLD. and Canberra, ACT), and under low and high disease pressure. In these tests, a hexaploid cross (Gos-5271) generated from a Fusarium-resistant G. sturtianum (Gos-5275) and a Fusarium-susceptible G. hirsutum L. (CPI-138969) was significantly more resistant to Fusarium wilt than its G. hirsutum parent. Thus G. sturtianum, with a diploid genome and a range of responses to Fov challenge, has the potential to provide the basis for the elucidation of the genetic basis of resistance to Fusarium wilt in cotton species. In addition, resistant accessions of G. sturtianum are identified as a potential source of Fusarium wilt resistance genes for cotton breeding. In the glasshouse tests used to assess the resistance of various Gossypium accessions to Fusarium wilt disease, the scoring of vascular browning was found to give a more reliable indication of disease severity than the scoring of foliar symptoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Trichome characteristics of F1Lycopersicon esculentum × L. cheesmanii f. minor and L. esculentum × L. pennellii hybrids and effects on Myzus persicae

Summary The green peach aphid (Myzus persicae) is a serious pest of the tomato (Lycopersicon esculentum). Trichome-based host plant resistance of wild Lycopersicon species may offer an alternative to pesticides for management of this pest. Two wild species, Lycopersicon cheesmanii f. minor and L. pennellii, were crossed with L. esculentum and the types and densities of trichomes possessed by the F₁ hybrids measured. The effects of these trichomes on M. persicae were assessed by placing nymphs on leaves and, 96 hr later, designating each nymph as either dead, alive, emigrating off the leaf or unaccounted for. A generalised linear model was used to detect relationships between the numbers of nymphs in each designation and the densities of trichomes and leaf area. Mortality of nymphs on L. pennellii hybrids was associated with high densities of type IV and low densities of type I trichomes. Mortality of nymphs on L. cheesmanii f. minor hybrids was associated with high densities of type III trichomes. An increase in the densities of type III trichomes on L. pennellii hybrids was associated with greater numbers of nymphs emigrating off the leaf whilst unaccounted nymphs on L. pennellii hybrids were associated with increased densities of type VII and type I trichomes. Further experimentation using excised leaflets found mortality on L. pennellii hybrids may be due to nymphs being hindered by type I trichomes and increased densities of type V trichomes were associated with greater numbers of unhindered nymphs. Implications of results are discussed in the context of introducing trichome-based host plant resistance into L. esculentum.     

Inheritance of tomato leaf curl virus resistance in Lycopersicon hirsutum f. glabratum

Summary Inheritance of resistance to tomato leaf curl virus (TLCV) was studied in the progenies derived from interspecific crosses between TLCV resistant Lycopersicon hirsutum f. glabratum line B 6013 and five susceptible cultivars (HS 101, HS 102, HS 110, Pusa Ruby and Punjab Chhuhara) of L. esculentum. P₁, P₂, F₁, F₂, B₁ and B₂ progenies of the five crosses were artificially inoculated with local strains of TLCV by means of the vector whitefly, Bemisia tabaci (Genn.). and the disease reaction was studied in all the crosses. Reaction of parents, F₁, F₂ and backcrosses suggests that resistance derived from L. hirsutum f. glabratum B 6013 is based on two epistatic genes, one from the wild parent and one from the cultivated one, resulting in a 13:3 segragation in the F₂.