Inheritance Pattern of Mungbean Yellow Mosaic Virus (MYMV) Disease Resistance in Blackgram [Vigna mungo (L.) Hepper]

Background: Mungbean yellow mosaic virus (MYMV) disease is the most destructive disease in blackgram. Development of MYMV resistant varieties is one of the best possible solutions to avoid the yield reduction in blackgram. There are conflicting reports on the genetics of resistance to MYMV disease claiming that it is controlled by both dominant and recessive genes. Hence the present study was aimed to understand the inheritance pattern of the MYMV disease resistance in eight crosses of blackgram.Methods: Parents, F1 and F2 generation of eight cross combinations were raised during July - Sep, 2018 at National Pulses Research Centre, Tamil Nadu Agricultural University, Vamban, Tamil Nadu. An infector row of CO 5 was raised to intensify the MYMV disease pressure after every eight rows. Based on disease incidence on 60th day after sowing, two phenotypic classes were formed among F2 plants with the scales of (1 to 3) as resistant phenotype and (4 to 9) as susceptible phenotype. The goodness of fit to Mendelian segregation ratio for MYMV disease resistance in the segregating population was tested by Chi square test (Stansfield, 1991).Result: The MYMV disease incidence was tri-genically controlled with inhibitory gene action in four crosses viz., MDU 1 x Mash 114, CO5 x Mash 114, MDU 1 x VBN 6 and CO 5 x VBN 6. Complementary gene action with two genes was observed in four crosses viz., MDU 1 x Mash 1008, CO 5 x Mash 1008, MDU 1 x VBN 8 and CO 5 x VBN 8. Differences in number of genes were observed due to the presence of recessive inhibitory gene in both male and female parents of the crosses which had complementary gene action for MYMV disease. The putative gene symbols assigned for the six genotypes viz., S1S1S2S2ii (MDU 1 and CO 5), s1s1s2s2II (Mash 114 and VBN 6) and s1s1s2s2ii (Mash 1008 and VBN 8), respectively.

Genetic analysis of various quantitative traits ininter-varietal crosses of Vigna mungo

Gene effects for 13 characters in four crosses of Vigna mungo were studied by six parameter generation mean model to determine the potential for the improvement of yield components. Scaling tests revealed inadequacy of the additive-dominance model for all the traits indicating the presence of non-allelic interactions. Duplicate gene action was observed for six characters in KUG-216 x HPBU-111, five in KUG-216 x Palampur-93, two in IPU-05-13 x Palampur-93 and one in IPU-05-13 x HPBU-111 and complementary gene action for one character each in KUG-216 x Palampur-93 and IPU-05-13 x HPBU-111 cross. Selection in later generations for duplicate gene action and early generation selection involving intermatings in F2 f or complementary gene action should be adopted for harnessing desirable recombinants.

Heterosis in lucerne testcrosses with Medicago arborea introgressions and Omani landraces and their performance in synthetics

Testcrosses were made with novel sources of lucerne germplasm. These were evaluated in the field in a subtropical environment to identify the lines which produced the highest yielding hybrids as a guide to future breeding efforts. The novel sources were derivatives of Medicago sativa × M. arborea partial (asymmetric) hybrids (termed sac) and very highly winter-active Omani landraces of M. sativa. As testers, 2 lines were used; a Colletotrichum trifolii race 2 resistant selection from the group 9 Australian-bred and adapted cultivar PacL 901 (selection hereafter termed 901) and the Omani landrace, Oman 2, collected at 17°N latitude, from Salalah, Oman. In the row experiment, substantial and significantly positive tester parent heterosis for overall yield (sum of 13 harvests) was observed in all of the sac × Oman 2 testcrosses, with the mean performance of the 11 testcrosses (1839 g/m row) significantly (P < 0.05) exceeding the mean performance of the sac × 901 testcrosses (1703 g/m row) evaluated. Where 901 was used as the tester, heterosis values relative to the tester for the same sac lines were negative for all testcrosses with 8 of the testcrosses being significantly negative. For the Omani landrace × 901 testcrosses, positive and negative heterosis values for total yield relative to the tester were observed, but none were significantly different from zero. The 901 tester yielded significantly (P < 0.05) more per se than the Oman 2 tester (1956 v. 1470 g/m row), although in an adjacent sward experiment Oman 2 yielded comparably to most of the standard commercial cultivars. The potential of the novel germplasm in the subtropics was verified in sward experiments with synthetics and/or strain crosses with yield increases of up to 42% over the benchmark synthetic Sequel. Further improvements can be expected following selection for disease and pest resistance within the lines and in the case of Oman 2 and sac, converging to maximise complementary gene action.

Prescreening Slash Pine and Cronartium Pedigrees for Evaluation of Complementary Gene Action in Fusiform Rust Disease

Single-urediniospore cultures of the fusiform rust fungus were used to inoculate seedlings from 10 full-sib families of a five-parent slash pine diallel at two different times in 1994. The presence or absence of fusiform rust galls was recorded for each inoculated seedling at 9 months postinoculation, and percent infection levels for each family-inoculum-time combination were used for detecting differences among host families and fungal cultures and for identifying differential interactions. The existence of differential interactions between two or more fungal cultures and two or more host families verifies that complementary gene action does exist in this pathosystem. Some host families may be excluded from more detailed interaction studies on the basis of their redundancy and lack of participation in differential interactions.

Inheritance of Albinism in Banana and Plantain (Musa spp.) and its Significance in Breeding

Few genetic markers are available in Musa spp. as a result of a lack of inheritance studies. Full-sib diploid (2n = 2x = 22) plantain-banana hybrids of the International Institute of Tropical Agriculture were selfed or outcrossed with other diploid bananas, one of which is an improved selection from Central America. Three populations having albinos (complete lack of chlorophyll in any plant tissue) were produced. The segregation ratios for albinism suggested that this deleterious trait is controlled by one or two recessive alleles. The small sample sizes (a problem inherent in the low reproductive fertility of cultivated parthenocarpic Musa) in two of these three populations did not allow for conclusiveness between the one or two genes model. However, a distinction was possible with the third population, consisting of 64 seedlings, of which four were albinos. The segregation ratio for albinism fit the 15:1 ratio (χ2 = 0.07, P = 0.79) and not the 3:1 ratio (χ2 = 11.02, P < 0.01), suggesting that albinism in Musa spp. is under the genetic control of at least two independent recessive alleles with complementary gene action. This finding also demonstrates that deleterious recessive alleles are present in the cultivated AAB plantain gene pool and in cultivated and advanced AA banana breeding populations. The latter suggests that population improvement through phenotypic recurrent selection for agronomic traits might be based on the elimination of deleterious recessive genes.

EVIDENCE FOR COMPLEMENTARY GENE ACTION CONFERRING RESISTANCE TO PUCCINIA GRAMINIS AVENAE IN AVENA SATIVA

Plants derived from a cross between the oat cultivar Kyto (Avena sativa L.) and A. sterilis L. were highly resistant to oat stem rust (Puccinia graminis Pers.) in the adult plant stage. This resistance was much superior to that of either parent. This is the first example of transgressive segregation in this host-parasite system. The genetic mechanism of this resistance is not completely understood but the resistance appears to be conferred by gene Pg-12 from Kyto interacting with a second gene. An alternate hypothesis is that a suppressor gene in Kyto prevents the resistance conditioned by Pg-12 from being expressed in the adult plant stage. This type of resistance is highly effective against all but two of the oat stem rust races known to occur in North America.