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The present study entitled “Genetic variability in Chinese potato (Solenostemon rotundifolius (Poir) J.K. Morton) for yield and nematode tolerance” was carried out in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani during 2017-2019, with the objective to identify high yielding Chinese potato genotypes having nematode tolerance. Chinese potato is a minor tuber crop of the tropics in which heavy yield loss occurs due to root knot nematode infestation.
The study comprised of two experiments. In the first experiment thirty accessions of Solenostemon rotundifolius (Poir) J.K. Morton, collected from ICAR - CTCRI Sreekariyam, local markets and farmers’ fields of major coleus growing tracts were evaluated for yield and nematode tolerance under field condition. These accessions were evaluated in Randomized Block Design (RBD) with thirty treatments and three replications during August 2018- January, 2019.
Analysis of variance was conducted for all the thirteen characters studied. For all characters except for point of tuberization and susceptibility to nematode infestation, ANOVA revealed significant differences among all the genotypes evaluated. The genotype Kenichira local (T17) recorded the highest tuber yield plant-1 (295.37g) followed by CP9 (261.67g), Suphala (258.10g) and CP 8 (254.05g) which were on par whereas the lowest yield of 123.32g was recorded by Thottamkulam local (T10). Minimum days to flowering, maximum number of tubers plant-1 and maximum harvest index were observed for the genotype Kenichira local (T17).
High genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were observed for tuber yield plant-1 and harvest index. Thus, selection for these characters would result in improvement of the genotype. High heritability coupled with high genetic advance was observed for number of tubers plant-1, tuber girth, tuber volume, average tuber weight, tuber yield plant-1, biological yield and harvest index. These characters, if selected for, would improve over generations.
Tuber yield plant-1 was significantly and positively correlated with number of tubers plant-1, tuber girth, average weight of tubers and harvest index both at genotypic and phenotypic levels. So an improvement in these characters would enhance the tuber yield plant-1. Path coefficients were found out using tuber yield plant-1 as the dependent character and other correlated characters as independent variables. Path analysis revealed that number of tubers plant-1, average weight of tubers and days to flowering had positive direct effect on tuber yield plant-1.
Mahalanobis’ D2 statistics was employed to study genetic divergence among the 30 genotypes which were grouped into ten clusters on the basis of relative magnitude of D2 values using Tocher’s method. Cluster I accommodated maximum number of genotypes and in sequence Clusters were having 7, 4, 4, 3,4, 3, 2, 1, 1 and 1genotypes respectively. The maximum inter-Cluster distance was observed between Clusters IV and VII. No close correspondence between geographical distribution and genetic divergence was observed.
The second experiment was pot culture study for varietal reaction to root knot nematode. The same thirty genotypes evaluated in experiment I were raised in Completely Randomized Design with three replications during July, 2018 to September 2018. All the pots were artificially inoculated with second stage juveniles of Meloidogyne incognita obtained from pure culture, at the rate of 1000 juveniles plant-1.
Nematode characteristics in both soil and root samples were studied. Maximum nematode population in soil was found in the genotype T8 (Parassala local 2). Root-knot index was calculated for each genotype based on scoring method suggested by Heald et al. (1989). According to this scoring method, the genotypes having 0-25 root knots per five gram of root was categorized as resistant. Fifteen genotypes were found to be in the category resistant. The genotype T11 (Pattambi local) showed highest mean values for number of larvae, root knot count, number of females and number of egg masses per five g root.
The results of the current study showed the presence of wide range of variability in the thirty Chinese potato genotypes. Characters such as number of tubers plant-1 and average weight of tubers had positive significant correlation and direct association with tuber yield plant-1. Considering superior yield with nematode resistance, Kenichira local ranked first. It was followed by Suphala, CP8 and Edayur local. Kenichira local, CP 28 and Edayur local can be forwarded for further yield trials for variety development.