Inheritance of black leaf mold resistance in tomato

Summary Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC₁F₂-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC₁F₂-358-4-13 and CL5915-93D₄-1-0-3). For each cross, six generations, i.e. P₁, P₂, F₁, F₂, BC₁F₁ and BC₁F₂ were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F₂ in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC₁F₂ data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.     

Identification of sources of resistance in Lycopersicon species to Tomato leaf curl geminivirus (ToLCV) by agroinoculation

A total of 90 genotypes of Lycopersicon species were tested forresistance to the Tomato leaf curlgeminivirus (ToLCV) by agroinoculation andthe vector whitefly (Bemisia tabaciGenn.) inoculation techniques underinsect-proof glasshouse conditions. Therate of infection in the inoculated plantswas determined by detection of the viralDNA in individual plants by the nucleicacid spot hybridization (NASH). Of the 38cultivars and 11 breeding lines of L.esculentum Mill. tested, none was highlyresistant or resistant while three andseven were moderately resistant whenexposed to the cloned virus DNAs byagroinoculation and whitefly inoculationrespectively. On the other hand, among the38 commercial cultivars screened, 16(42.1%) were highly susceptible in vectorinoculations and 31 (81.6%) inagroinoculation. Among the exoticcollection (EC) accessions six were highlyresistant, eleven resistant to whiteflyinoculation and none was highly susceptiblein either of the two tests, indicating thepresence of resistance among the ECaccessions. A higher degree of resistancewas observed in other species of Lycopersicon. While only one accession ofL. cheesmanii Riley was tested, itcould not be infected by either of the twomethods. L. pimpinellifolium (Jusl.)Mill. genotype EC 251580 was similarlyresistant. In L. peruvianum (L.)Mill., five EC accessions could not beinfected by whitefly inoculation, withthree of these being resistant and twomoderately resistant in agroinoculation.This study demonstrates the importance ofthe agroinoculation technique in the virusresistance screening programs andidentifies several good sources ofresistance to the Tomato leaf curlvirus in Lycopersicon species.     

Resistance in two Lycopersicon species to an Arkansas isolate of tomato spotted wilt virus

Summary Tomato spotted wilt virus (TSWV) was obtained from infected tomatoes in commercial fields in Arkansas in 1985. A greenhouse screening procedure for identifying tomatoes resistant to TSWV was established using an enzyme-linked immunosorbent assay (ELISA) to detect infected plants. Symptom expression was variable and symptom expression was not reliable for identifying infected plants. Germplasm evaluated for resistance to one typical Arkansas isolate (85–9) of TSWV included: twenty cultivars and breeding lines of Lycopersicon esculentum Mill, 52 accessions of L. pimpinellifolium (Jusl.) Mill and 8 accessions of L. peruvianum (L.) Mill. All cultivated accessions and breeding lines evaluated were susceptible. Some individual plants in several accessions of L. pimpinellifolium were resistant and nearly all plants of the L. peruvianum accessions that were evaluated were resistant to isolate 85–9.Dept. of Plant Pathology     

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.     

Reaction of Lycopersicon cultivars and wild accessions to tomato leaf curl virus

Summary 1201 tomato cultivars, breeding lines and accessions of Lycopersicon species were screened for tomato leaf curl virus (TLCV) under field and laboratory conditions during summer seasons of 1986 to 1989. Two lines of L. hirsutum (PI 390658 and PI 390659) and 2 lines of L. peruvianum (PI 127830 and PI 127831) were resistant to TLCV infection. These accessions did not produce any leaf curl symptoms either in field or after inoculation by whitefly Bemisia tabaci with TLCV. Adult whiteflies died within 3 days after releasing on resistant accessions (PI 390658, PI 390659, PI 127830), whereas the whiteflies survived upto 25 days on susceptible tomato cultivars. Under field conditions 0–4 and 5–25 adult whiteflies were observed on resistant and susceptible cultivars respectively. Hybridization was effected using the popular tomato cultivars Arka Sourabh, and Arka Vikas, as the female parents and the resistant Lycopersicon wild species as the pollen parents, to incorporate the resistant gene(s) into the edible tomatoes.     

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.     

Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) in Lycopersicon species

Summary Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) were investigated in 16 accessions of three Lycopersicon species and 55 commercial tomato hybrids and cultivars. All commercial hybrids and cultivars were highly susceptible. Accessions of L. hirsutum, L. hirsutum f. glabaratum and L. pimpinellifolium showed a wide range of reactions. Those of L. peruvianum, LA 385 of L. peruvianum f. humifusum exhibited very high levels of resistance indicating their potential use in local breeding programs. In contrast to earlier findings, back indexing showed that all symptomless genotypes in this investigation were carriers of the TYLCV.     

Quantitative resistance to Cercospora leaf spot disease caused by Pseudocercospora cruenta in cowpea

Six populations (Parent 1, Parent 2, F1, F2, BC1 and BC2) generated from each of four crosses involving four resistant and two susceptible varieties of cowpea (Vigna unguiculata L. Walp) were evaluated for resistance to Cercospora leaf spot (CLS) disease caused by Pseudocercospora cruenta under induced epiphytotic conditions, in four separate field experiments. Climatic conditions determined the onset of CLS disease in the susceptible cultivar and varied in the four experiments from 35 to 48 days after planting (DAP). Genetic analysis revealed that the mode of inheritance of resistance to P. cruenta can be oligogenic or polygenic depending upon the cross. This is the first report of polygenic inheritance of CLS resistance. Number of nodes infected fitted a simple additive dominance model with predominance of additive effects based on generation mean analysis. Oligogenic resistance was observed for the other three crosses, with the most plausible models being: a single gene model with incomplete dominance in CB27 × IT87D-939-1; a single gene model with complete dominance in CB27 × VRB-10; and a triger model in Los Banos Bush Sitao × IT86D-792, based on segregation analysis of symptomatic : non-symptomatic plants. The role of minor genes was also indicated in the above crosses. Suggested approaches to breeding for resistance to CLS are discussed.     

Evaluation of seven Lycopersicon species for resistance to tomato spotted wilt virus (TSWV)

Summary One hundred eighty-eight accessions of Lycopersicon cheesmanii, L. chilense, L. chmielewskii, L. hirsutum, L. parviflorum, L. pennellii, and L. peruvianum were screened for resistance to three isolates of tomato spotted wilt virus (TSWV). All plants in an accession were initially screened for resistance to TSWV using isolate 85–9 from Arkansas. Visual symptoms were used to cull obviously infected plants, followed by enzyme-linked immunosorbent assay (ELISA) to identify uninfected plants. Cuttings were taken from uninfected plants in the first screening and the resulting plants were inoculated with isolates Glox and T-2 from Texas and Hawaii, respectively. No resistance was identified in L. cheesmanii, L. chmielewskii, L. hirsutum, L. parviflorum, and L. pennellii. However, 33 of 63 L. chilense accession produced 91 of 1268 plants that were uninfected with isolate 85–9 and 20 accessions that produced 40 of 257 plants that were not infected with any of the isolates. After screening with isolate 85–9 9 of 12 L. peruvianum accessions tested had 38 plants uninfected and 8 accessions had 25 plants that were not infected with any of the isolates.     

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.     

High salt tolerance potential in Lycopersicon species during germination

Summary The potential to improve seed germination responses to salinity was evaluated for 13 accessions representing six wild Lycopersicon species and 20 accessions of L. esculentum. Germination response times increased in all accessions at 100 mM NaCl. Analysis indicated that one accession of L. peruvianum (PI126435) germinated faster under high salinity than all other accessions and was closely followed by L. pennellii (LA716). The fastest germinating L. esculentum accession, PI174263, ranked third. Additional wild ecotypes exhibiting rapid germination at 100 mM NaCl were identified among L. pimpinellifolium and L. peruvianum.     

Resistance to tomato spotted wilt virus in transgenic tomato hybrids

Summary Tomato spotted wilt virus (TSWV) causes significant economic losses in the commercial culture of tomato (Lycopersicon esculentum Mill.). Culture practices and introgression of natural sources of resistance to TSWV have only been marginally effective in controlling the TSWV disease. Recently however, high levels of protection against TSWV have been obtained by transforming tobacco with a chimaeric gene cassette comprising the TSWV nucleoprotein gene. This report demonstrates the successful application of this newly-created TSWV resistance gene in cultivated tomato. Transformation of an inbred tomato line with the TSWV nucleoprotein gene cassette resulted in high levels of resistance to TSWV that were maintained in hybrids derived from the parental tomato line. Therefore, transformant lines carrying the synthetic TSWV resistance gene make suitable progenitors for TSWV resistance to be incorporated into the breeding programmes of tomato.     

Resistance to Corynebacterium michiganense in tomato genotypes

Summary The highest level of resistance to Corynebacterium michiganense was found in Irat L3 and Okitsu Sozai 1–20. Resistance was partial and symptomless plants proved to be carriers of the disease. The resistance is at least partially based on a diminished multiplication of the pathogen in the host plant.     

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.     

Brassica coenospecies: a rich reservoir for genetic resistance to leaf spot caused by Alternaria brassicae

Development of leaf spot resistant mustard cultivars is a relevant objective in view of heavy crop losses caused by this pathogen. Thirty-eight species belonging to 9 genera, including cultivated and wild allies, of the genus Brassica were evaluated under epiphytotic conditions for two years. Inoculations were done on whole plants (in vivo) and on detached leaves (in vitro). Data on incubation period, number of lesions per leaf, lesion size and leaf area covered by lesions were recorded. Species which never produced disease symptoms throughout the growing period in pots and until 72 hours after inoculation in detached leaf assays during both years were treated as resistant, while those that produced symptoms were classified as moderately resistant, susceptible or highly susceptible depending upon incubation period, size of lesions and leaf area covered by disease symptoms. Eight species (Brassica desnottesii, Camelina sativa, Coincya pseuderucastrum, Diplotaxis berthautii, D. catholica, D. cretacea, D. erucoides, and Erucastrum gallicum) were found completely resistant, whereas others were classified as moderately resistant (12), susceptible (11) or highly susceptible (9). Since resistance is unavailable within the cultivated species, these 8 resistant wild species could be used as donor parents for introgressing resistance to leaf spot disease in Indian mustard. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Genetic analysis of resistance to bacterial leaf streak caused by Xanthomonas campestris pv. undulosa in bread wheat

Summary The inheritance of resistance to bacterial leaf streak or black chaff of wheat was studied under field conditions, with an artificial epidemic of Xanthomonas campestris pv. undulosa. A complete series of crosses between five parents, differing in reaction to X. c. pv. undulosa, was generated. Disease was recorded at two different stages of growth. No evidence of cytoplasmic effect was found from the comparison between reciprocal F₁ crosses. The study of the F₃ generations attested that five genes were involved in resistance to bacterial leaf streak. Separate analyses carried out for the two scoring dates were mutually consistent: genotypes, number of genes, and their action and relative importance were verified. The genes differed in strength of expression of resistance. One of the two strongest genes, Bls1, is present in all three superior parents, Pavon 76, Mochis T88 and Angostura F88. Resistance was not complete, and proved to be stable over the season.     

The response to temperature of leaf area in tomato genotypes. II. The rate of leaf production

Summary Genotypic variation in the response to temperature of the rate of leaf production is reported. Leaf production was measured as the rate of successive leaves passing a specific length and by dissecting plants to obtain the rate of leaf initiation. These results together with the results of leaf size from the previous paper. are compared to the effect of temperature on the total leaf area. The use of information from these experiments in selecting for increased leaf area at low temperature is discussed.Guestworker Project Group Tomato Physiology.     

Inheritance of resistance to the bipartite Tomato chlorotic mottle begomovirus derived from Lycopersicon esculentum cv. ‘Tyking’

Severe outbreaks of bipartite begomoviruses (family Geminiviridae) have been observed on tomatoes after the introduction of the whitefly Bemisia tabaci (biotype B) in Brazil. The Lycopersicon esculentum line ‘TX 468-RG’ was identified as one of the best sources of broad-spectrum resistance to species comprising the tomato-infecting Begomovirus complex in Brazil. The genetic basis of resistance to one Begomovirus isolate was investigated using populations from the cross between ‘TX 468-RG’ (P₁) and the susceptible line ‘Ohio 8245’ (P₂). Parental lines, F₁, backcross (BC) to P₁ and BC to P₂ and F₂ generations were inoculated at the two true-leaf stage using 20 viruliferous whiteflies per plant. Assessment was done two weeks after inoculation based upon visual analysis of symptom expression. The ratio of resistant to susceptible plants closely fit to a single recessive gene (locus) model. The sequence analysis indicated that the Begomovirus isolate used in this assay was closely related to the bipartite Tomato chlorotic mottle virus. Therefore, this gene/locus, was tentatively named tcm-1 (tomato chlorotic mottle virus resistance-1). This locus has been transferred to distinct tomato cultivars and levels of resistance similar to that of ‘TX 468-RG’ were observed in advanced (F₈ and F₉) generations. In addition, breeding lines carrying the tcm-1 locus were also resistant to other Brazilian bipartite tomato-infecting Begomovirus species.     

Mite responses in relation to trichomes of Lycopersicon esculentum x L. hirsutum F2 hybrids

Summary Leaflets from 11 L. esculentum x L. hirsutum F₂ individuals were bioassayed with spider mites (Tetranychus urticae). Densities of Type I, Type III, Type IV, Type V, and Type VI trichomes and the intensity of red fluorescence of the Type VI trichome tip varied widely among the 11 F₂ hybrids. Mite responses were analyzed in relation to these trichome characters and leaflet surface. Variation in Type IV density accounted for most of the variation in mite responses. Densities of Type I, V and VI trichomes also contributed to mite responses but their effects were obscured by high Type IV densities. Type VI tip fluorescence was not associated with responses of mites in bioassays of these hybrids.The investigation reported in the paper (84-10-123) 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)