Inheritance of resistance to the chlorosis component of tan spot of wheat caused by Pyrenophora tritici-repentis, races 1 and 3

The fungus Pyrenophora tritici-repentis, causal agent of tan spot of wheat, produces two phenotypically distinct symptoms, tan necrosis and extensive chlorosis. The inheritance of resistance to chlorosis induced by P. tritici-repentis races 1 and 3 was studied in crosses between common wheat resistant genotypes Erik, Hadden, Red Chief, Glenlea, and 86ISMN 2137 and susceptible genotype 6B-365. Plants were inoculated under controlled environmental conditions at the two-leaf stage and disease rating was based on presence or absence of chlorosis. In all the resistant × susceptible crosses, F₁ plants were resistant and the segregation of the F₂ generation and F₃ families indicated that a single dominant gene controlled resistance. Lack of segregation in a partial diallel series of crosses among the resistant genotypes tested with race 3␣indicated that the resistant genotypes possessed␣the same resistance gene. This resistance gene was effective against chlorosis induced by P.␣tritici-repentis races 1 and 3.     

Inheritance of downy mildew resistance in Indian cauliflower (group III)

Summary Inheritance of downy mildew (Peronospora parasitica) resistance in three resistant x susceptible crosses, one susceptible x susceptible and one resistant x resistant cross were studied in Indian cauliflower (Group III) over the two years (1990 and 1991). No significant difference was observed between the years for various estimates and hence pooled data are presented. Downy mildew resistance in crosses cc×HR 5-4 and 3-5-1-1×244 (R×S) is governed by single dominant gene PPA3 but in cross cc×244 (R×S), recessive epistasis was observed. The resistance level was not improved in both the cc×3-5-1-1 (R×R) and 244×267-6-9 (S×S) crosses. Exploitation of downy mildew resistance from cc and 3-5-1-1 in F₁ hybrid is explained in detail.     

Genetical analysis of resistance to Mycosphaerella pinodes in pea seedlings

Summary In studies of the inheritance of resistance, pea seedlings of seven lines in which stems and leaves were both resistant to Mycosphaerella pinodes were crossed with a line in which they were both susceptible. With seven of the crosses resistance was dominant to susceptibility. When F₂ progenies of five crosses were inoculated on either stems or leaves independently, phenotypes segregated in a ratio of 3 resistant: 1 susceptible indicating that a single dominant gene controlled resistance. F₂ progenies of one other cross gave ratios with a better fit to 9 resistant: 7 susceptible indicating that two co-dominant genes controlled resistance. The F₂ progeny of another cross segregated in complex ratios indicating multigene resistance.When resistant lines JI 97 and JI 1089 were crossed with a susceptible line and leaves and stems of each F₂ plant were inoculated, resistance phenotypes segregated independently demonstrating that leaf and stem resistance were controlled by different genes. In two experiments where the F₂ progeny of the cross JI 97×JI 1089 were tested for stem and leaf resistance separately, both characters segregated in a ratio of 15 resistant:1 susceptible indicating that these two resistant lines contain two non-allelic genes for stem resistance (designated Rmp1 and Rmp2) and two for leaf resistance (designated Rmp3 and Rmp4). Evidence that the gene for leaf resistance in JI 1089 is located in linkage group 4 of Pisum sativum is presented.     

Identification of alleles at two loci controlling resistance to Phomopsis stem blight in narrow-leafed lupin (Lupinus angustifolius L.)

The genetics of resistance to Phomopsis stem blight caused by Diaporthe toxica Will., Highet, Gams & Sivasith. in narrow-leafed lupin (Lupinus angustifolius L.) was studied in crosses between resistant cv. Merrit, very resistant breeding line 75A:258 and susceptible cv. Unicrop. A non-destructive glasshouse infection test was developed to assess resistance in the F₁, F₂, selected F₂-derived F₃ (F_2:3) families, and in selfed parent plants. The F₁ of Unicrop × 75A:258 (and reciprocal cross) was very resistant, and the F₂ segregated in a ratio of 3:1 (resistant: susceptible), which suggested the presence of a single dominant allele for resistance in 75A:258. In Merrit × Unicrop (and reciprocal), the F₁ was moderately resistant, and the F₂ segregated in a ratio of 3:1 (resistant: susceptible). Thus Merrit appeared to carry an incompletely dominant resistance allele for resistance. The F₁ of Merrit × 75A:258 (and reciprocal) was very resistant and the F₂ segregated in a ratio of 15:1 (resistant: susceptible), which supported the existence of independently segregating resistance alleles for resistance in 75A:258 and Merrit. Alleles at loci for early flowering (Ku) and speckled seeds (for which we propose the symbol Spk) segregated normally and independently of the resistance alleles. Resistant F₂ plants gave rise to uniformly resistant or segregating F_2:3 families, whereas susceptible F₂ plants gave rise only to susceptible F_2:3 families. However, the variation in resistance in the F₂ and some F_2:3 families of crosses involving 75A:258, from moderately to extremely resistant, was greater than that expected by chance or environmental variation. We propose the symbols Phr1 to describe the dominant resistance allele in 75A:258, and Phr2 for the incompletely dominant resistance allele in Merrit. Phr1 appears to be epistatic to Phr2, and expression of Phr1 may be altered by independently segregating modifier allele(s). This revised version was published online in July 2006 with corrections to the Cover Date.     

Resistance of lettuce (Lactuca) to the leaf aphid Nasonovia ribis nigri. 2. Inheritance of the resistance

Summary The inheritance of resistance to Nasonovia ribis nigri in L. sativa was investigated. Parents and F₁ and F₂ populations from crosses between the susceptible cultivar Ravel and two resistant breeding lines were tested. In both breeding lines one dominant gene appeared responsible for resistance.     

Inheritance of resistance to angular leaf spot in Nicotiana tabacum L. cultivars burley 21 and kentucky 14

Summary The genetics of resistance to angular leaf spot caused by Pseudomonas syringae pv. tabaci in Nicotiana tabacum cultivars Burley 21 and Kentucky 14 was investigated by studying disease reactions to three isolates of parental, F₁, F₂ and backcross generations derived from crosses between the resistant cultivars and the susceptible cultivar Judy's Pride. Studies were conducted in the greenhouse and in field plant beds. Chi-square values were computed to determine whether the observed ratios for disease reactions deviated from expected Mendelian ratios for a single, dominant gene controlling resistance to angular leaf spot in tobacco. Based on the resistance of the F₁ and the backcross generation to the resistant parent (BC-R), a 3 resistant: 1 susceptible segregation ratio in the F₂, and a 1 resistant: 1 susceptible segregation ratio in the backcross generation to the susceptible parent (BC-S), it was concluded that resistance to three isolates of Pseudomonas syringae pv. tabaci is governed by a single, dominant gene.     

Response to selection for high and low partial resistance to leaf blast in F2 populations of three rice crosses

Summary Divergent selection for higher and lower partial resistance to leaf blast was applied in F₂ populations of crosses between the rice cultivars IR36, IR64 and CO39 after exposure to a virulent isolate. IR36 and IR64 are partially resistant while CO39 is highly susceptible. As selection criteria the number of sporulating lesions in leaves of the main culm or the lesion density in the topmost leaf relative to other F₂ plants with the same stage of development were used. A highly significant and meaningful response to selection was obtained in most cases, but the heritability was low. Realized heritabilities varied from 0.14 to 0.25 depending on the cross and were similar for both selection criteria. Selection for improved partial resistance to leaf blast is possible as early as the F₂. The efficiency of selection is probably much higher if replicated tests could be made, and better results are therefore expected if selection among F₃ lines is carried out. The results indicated that the relatively low infection efficiency in IR36 and IR64 is oligo- or polygenically controlled.     

Genetics of disease resistance in urdbean (Vigna mungo (L.) Hepper) to the leaf spots caused by Colletotrichum truncatum (Schw.) Andrus & Moore

Summary The resistance sources among various test cultivars of urdbean to Colletotrichum truncatum, a leaf spotting pathogen, were identified and genetics of resistance was worked out by studying F₁, F₂ and F₃ generations of crosses between resistant cultivars and the susceptible cv. Kulu 4 and of those among the resistant parents. The resistance was found to be controlled by single dominant genes and the resistance genes were non-allelic.     

Root pulling resistance in rice: Inheritance and association with drought tolerance

Summary Avoidance of drought stress is commonly associated with root system characteristics and root development. The inheritance of root pulling resistance in rice (Oryza sativa L.) was investigated and its relationship with visual field scores for drought tolerance was studied. Transgressive segregation for high root pulling resistance was observed in 3 crosses (high x high, low x high, and intermediate x intermediate). Both dominant and additive genes control the variation. F₁ superiority for high root pulling resistance was observed and could be exploited in an F₁ hybrid breeding program. F₂ distribution curves indicated that plants highly resistant to root pulling can be obtained not only from low x high and high x high crosses, but also from intermediate x intermediate crosses. Root pulling resistance in rice has a low heritability (39 to 47%). Thus, breeding for a high root pulling resistance may best be accomplished by selection based on line means rather than individual plant selection. Field screening showed significant differences in leaf water potential among random F₃ lines. F₃ lines with higher leaf water potential had better visual scores for drought tolerance. Visual drought tolerance scores were correlated with root pulling resistance. Plants with high root pulling resistance had the ability to maintain higher leaf water potentials under severe drought stress. The usefulness of the root pulling technique in selecting drought tolerant genotypes was confirmed.     

Inheritance of resistance to pea blight (Ascochyta pinodella) and induction of resistance in pea (Pisum sativum L.)

Summary Pea blight caused by Assochyta pinodella does considerable damage to the pea crop every year. To ascertain the inheritance of resistance to pea blight and incorporate resistance in the commercial cultivars, crosses were made between Kinnauri resistant to pea blight and four highly susceptible commercial pea cultivars — Bonneville, Lincoln, GC 141 and Sel. 18. Studies of the F₁'s, F₂'s, back crosses and F₃'s indicated that Kinnauri carries a dominant gene imparting resistance to pea blight.     

Genetics of resistance to Aphis craccivora in cowpea

Summary Inheritance of aphid resistance and allelic relationships among sources of resistance was studied in the parents, F₁, F₂, F₃, and backcross populations of cowpea crosses. Each 4-day old seedling was infested with five fourthinstar aphids. Seedling reaction was recorded 14–16 days after infestation when the susceptible check was killed. The segregation data from eight crosses between resistant and susceptible cowpea cultivars indicated that aphid resistance was inherited as a monogenic dominant trait. Segregation data from crosses among eight resistant cultivars indicated that one or two loci and modifier(s) were involved in the expression of resistance to aphids. It was suggested that further studies on allelism among sources of resistance needed to be conducted in order to resolve this.     

Partial resistance of barley to leaf rust,Puccinia hordei. III. The inheritance of the host plant effect on latent period in four cultivars

Summary The latent period (LP) in the barley-leaf rust relationship is an important component of the partial resistance complex. The inheritance of the host plant effect on LP was studied in five crosses between four cultivars. The LP, effectuated by the susceptible cultivars L94 and L92, were 8.0 and 8.6 days resp., those of the resistant cultivars Minerva (Mi) and Vada (Va) 16.9 and 17.1 days resp. The mean F₁ and F₂ values of the crosses L92×L94 and Mi x Va were intermediate between the parental ones. The variances of the F₂'s were slightly larger than those of the parents and the F₁'s indicating some segregation. In the crosses between a susceptible and a resistant cultivar the F₁ value was half way between the mid-parent and susceptible parent value. The F₂ mean lay approximately half way between the mid-parent and F₁ value, with a distribution positively skewed and slightly bimodal. There was no transgression, in fact not even the parental values were recovered among nearly 500 F₂ plants. The F₃-lines of the crosses between susceptible and resistant cultivars showed within line variances from as low as the parental values to as high as or higher than those of the F₂. In hte F₃'s the parental values could be recovered although no transgression occurred.L94 is supposed to carry no genes effecting a longer LP. The long LP of Mi and Va, assuming no linkage, is thought to be effectuated by the cumulative action of a recessive gene with a fairly large effect and some four to five minor genes with additive inheritance. One of these minor genes is supposed to be carried by L92, while Mi and Va are thought to differ for one minor gene only. In case linkage exists, the number of minor genes involved could be higher.     

Inheritance of reaction to Pseudomonas lachrymans in pickling cucumber

Summary Cucumber (Cucumis sativus) lines resistant to angular leafspot caused by Pseudomonas lachrymans react to an infection by developing necrotic lesions that lack the chlorotic halo characteristic of the susceptible reaction. The inheritance of the non-halo lesion reaction was studied in all possible crosses between resistant lines MSU 9402 and Gy 14A, and susceptible cultivars Wisc. SMR 18 and National Pickling. Genetic analysis of the F₁, F₂, backcross and F₃ populations revealed that the non-halo lesion type, associated with resistance, was controlled by a single recessive gene, pl. This character appears to be an important component of resistance to P. lachrymans.     

Inheritance of seed resistance to bruchids in cultivated mungbean (Vigna radiata, L. Wilczek)

Bruchid beetles or seed weevils are the most devastating stored pests of grain legumes causing considerable loss to mungbean (Vigna radiata (L.) Wilczek). Breeding for bruchid resistance is a major goal in mungbean improvement. Few sources of resistance in cultivated genepool were identified and characterized, however, there has been no study on the genetic control of the resistance. In this study, we investigated the inheritance of seed resistance to Callosobruchus chinensis (L.) and C. maculatus (F.) in two landrace mungbean accessions, V2709BG and V2802BG. The F₁, F₂ and BC generations were developed from crosses between the resistant and susceptible accessions and evaluated for resistance to the insects. It was found that resistance to bruchids in seeds is controlled by maternal plant genotype. All F₁ plants derived from both direct and reciprocal crosses exhibited resistance to the bruchids. Segregation pattern of reaction to the beetles in the F₂ and backcross populations showed that the resistance is controlled by a major gene, with resistance is dominant at varying degrees of expressivity. Although the presence of modifiers was also observed. The gene is likely the same locus in both V2709BG and V2802BG. The resistant gene is considered very useful in breeding for seed resistance to bruchids in mungbean.     

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.     

Inheritance of resistance to black rot (Xanthomonas campestris pv. Campestris) in cauliflower (Brassica oleracea var. Botrytis)

Summary Black rot disease caused by Xanthomonas campestris pv. campestris is a limiting factor in the commercial production of the cauliflower crop. Crosses were attempted between SN 445, a mid season cultivar resistant to black rot and two highly susceptible commercial cultivars (Pusa Snowball-1 and K-1). Studies of the F₁'s, F₂'s and back crosses indicated that SN 445, carries a dominant gene imparting resistance to black rot.     

The inheritance of resistance to beet necrotic yellow vein virus (BNYVV) in B. vulgaris subsp. maritima, accession WB42: Statistical comparisons with Holly-1-4

In this study, the inheritance of resistance to Beet necrotic yellow vein virus (BNYVV) in accessions Holly-1-4and WB42 was investigated. Crosses between both resistant sources and susceptible parents were carried out and F₁F₂ and BC₁ populations were obtained. Virus concentrations in WB42and its F₁ populations were lower than in Holly-1-4. Observed ratios of susceptible and resistant plants in segregating populations of Holly-1-4 as well as WB42 were in agreement with hypothesis of one dominant major gene. Segregation of plants in F₂ populations obtained from crosses betweenHolly-1-4 and WB42 revealed that the resistance genes in Holly-1-4 and WB42 were nonallelic and linked loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Identification of segregation-distortion-neutral alleles to improve pollen fertility of indica-japonica hybrids in rice (Oryza sativa L.)

The genetics of resistance to Ascochyta blight (Ascochyta fabae f. sp. fabae) was studied in two populations of faba bean (Vicia faba). Plants of a resistant population, ILB 752, and a susceptible one, NEB 463, were screened for their reaction to the pathogen and the results were quantified on a scale of 0–5. Crosses were made between plants both within and between accessions and the F₁ and F₂ generations assessed in a field trial 21 and 45 days after inoculation. Disease scores were greater at 45 days than at 21 days and they were not significantly affected by the presence of susceptible spreader rows in part of the trial. ILB 752 carried a major dominant gene conferring resistance while NEB 463 carried the recessive allele for susceptibility. Furthermore, a minority of plants of NEB 463 appeared to carry at least one pair of complementary recessive genes, also conferring resistance. Most of the plants of ILB 752 were homozygous for the dominant resistance gene and a few were heterozygous. Reciprocal crosses behaved identically, indicating the absence of maternal effects in the expression of Ascochyta blight resistance in faba beans. The results show that it is important to confirm the level of heterozygosity for the resistance genes in this partially outbreeding species before crossing is commenced. The major dominant gene for resistance, identified in ILB 752, has clear potential for use in breeding for Ascochyta blight resistance. The minor genes identified in NEB 463 also show the potential for accumulating resistance through mass selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of resistance to Fusarium head blight caused by Fusarium graminearum in Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165

The genetic constitution of resistance to Fusarium head blight (FHB, scab) caused by Fusarium graminearum in the Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165 was investigated using doubled haploid lines (DHLs) and recombinant inbred lines (RILs). Frequency distributions of DHLs derived from two F₁ crosses, Sumai 3 (very resistant to resistant; VR-R) / Gamenya (very susceptible; VS) and Sumai 3 / Emblem (VS), fitted well to 1: 2: 1 (resistant: moderately resistant: susceptible) ratios for reaction to FHB in the field. It is suggested that the resistance of Sumai 3 is controlled by two major genes with additive effects. One of the resistance genes may be linked in repulsion to the dominant suppressor B1 for awnedness with recombination values 15.1 ± 3.3% in Sumai 3 /Gamenya and 21.4 ± 4.3% in Sumai 3 / Emblem. Saikai 165 is a Japanese resistant line derived from an F₁ Sumai 3 / Asakaze-komugi (moderately resistant; MR). The data for RILs derived from the cross Emblem / Saikai 165, indicates that three resistance genes control the resistance of Saikai 165. This revised version was published online in July 2006 with corrections to the Cover Date.