Genetic Diversity, Identification, and Utilization of Novel Genetic Resources for Resistance to Meloidogyne incognita in Mulberry (Morus spp.).

Mulberry (Morus spp.) is an important crop in the sericulture industry, as the leaves constitute the primary feed for the silkworm. The availability of diverse genetic sources of resistance to root-knot nematode (RKN; Meloidogyne spp.) are very scanty. To address this need, a set of 415 varied exotic and indigenous germplasm accessions were screened under glasshouse conditions. Twenty-one accessions were identified as highly resistant and 48 were resistant, with the highest numbers of highly resistant/resistant accessions being found in Morus alba. Further, 30 accessions based on rooting ability were evaluated for field resistance at four different locations with infested soil. Finally, eight germplasm accessions (BR-8, Karanjtoli-1, Hosur-C8, Nagalur Estate, Tippu, Calabresa, Thai Pecah, and SRDC-3) were identified as potential genetic sources in RKN-resistance breeding programs or as resistant rootstock for the establishment of mulberry gardens. Sixteen simple sequence repeat markers analyzed among the 77 resistant and susceptible accessions generated 55 alleles, ranging from two to five, with an average of 3.43 alleles per locus. Principal coordinates analysis grouped the accessions on the basis of susceptibility and resistance to RKN infestation. The RKN-susceptible accessions exhibited higher variability as compared with resistant accessions, and they were more dispersed. Analysis of molecular variance showed maximum molecular variance was 78% within the population, and 22% between populations. Results of this study indicate that simple sequence repeat markers are reliable for assessing genetic variability among the RKN-resistant and RKN-susceptible mulberry accessions.

Characterization and Pathogenicity of Lasiodiplodia theobromae Causing Black Root Rot and Identification of Novel Sources of Resistance in Mulberry Collections.

Black root rot (BRR) caused by Lasiodiplodia theobromae is an alarming disease of mulberry that causes tremendous economic losses to sericulture farmers in India and China. Successful control of this disease can be attained by screening germplasm and identifying resistant sources. Seventy four diseased root samples were collected from farmer's fields belonging to four major mulberry growing states of South India. Based on morpho-cultural and scanning electron microscopy studies, 57 fungal isolates were characterized and identified as L. theobromae. Phylogenetic analysis of concatenated internal transcribed spacer and ß-tubulin sequences revealed variation of the representative 20 isolates of L. theobromae. Following the root dip method of inoculation, pathogenicity studies on susceptible mulberry genotypes (Victory-1 and Thailand male) recognized the virulent isolate MRR-142. Accordingly, MRR-142 isolate was used to evaluate resistance on a set of 45 diverse mulberry accessions. In the repeated experiments, the mulberry accession ME-0168 which is an Indonesian origin belonging to Morus latifolia was found to be highly resistant consistently against BRR. Eight accessions (G2, ME-0006, ME-0011, ME-0093, MI-0006, MI-0291, MI-0489, and MI-0501) were found to be resistant. These promising resistant resources may be exploited in mulberry breeding for developing BRR resistant varieties and to develop mapping populations which successively helps in the identification of molecular markers associated with BRR.

Molecular profiling of blast resistance genes and evaluation of leaf and neck blast disease reaction in rice.

In the present investigation, phenotypic evaluation of blast disease reaction was conducted at Ponnampet and Mandya districts of Karnataka, India, which indicated that the rice varieties such as IR64, Jaya, KMP153, IR30864, Mandya Sona-1, Mandya Sona-2, KCP-1, Dodda Byra, and Malgudi Sanna were susceptible to both leaf and neck blasts. Further, the rice varieties that were resistant to leaf blast such as KMP200, DHMAS70Q164-1b, Karibatta, Coimbatore Sanna and others showed susceptible reaction to neck blast only. In contrast, the varieties such as JyothixBR2655, Punkutt Kodi, Sirsi, 222 and Gangadale which were resistant to neck blast were found to be susceptible to leaf blast also. Only one variety, BR2655 showed resistance to both leaf and neck blast diseases. The genotypic studies using simple sequence repeat markers showed that the analysis of the distribution of resistance genes and genotyping of the selected rice varieties, and traditional rice varieties from different ecological regions with allele specific markers helped to identify 20 major blast resistance genes. The individual gene frequencies of the 20 major rice blast resistance genes varied from 10.34 to 100%. Less and more frequency of resistance gene distribution occurred in Pi9 and Pizt gene, respectively. The result of this study would help to create strategies for improving rice blast resistance through genetic studies and plant-pathogen interaction.