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ThesisItem Embargo Genetic diversity analysis for nutrient efficiency and identification of nutrient responsive genes in cassava (Manihot esculenta Crantz)(Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2023-02-10) Swathy Sivan; KAU; Arya, KThe present study entitled “Genetic diversity analysis for nutrient efficiency and identification of nutrient responsive genes in cassava (Manihot esculenta Crantz)” was carried out in the Department of Plant breeding and Genetics, College of Agriculture, Vellayani and Division of Crop Improvement, ICAR-CTCRI, Sreekariyam, during 2019-2022. The study was undertaken to screen and characterize N and K-efficient genotypes in cassava and identify the traits contributing to nutrient efficiency and study their gene expression. Thirty genotypes of cassava comprising of landraces, released varieties and pre-release accessions from ICAR-CTCRI and KAU were taken for the study. Field evaluation was done to identify low input nutrient efficient lines where analysis of variance revealed significant difference among the genotypes for all the characters studied except the girth of tuber. High GCV, PCV, heritability and genetic advance were observed for traits like tuber yield, N and K efficiency, plant height, number of leaves, number of branches, stem N and K content. Tuber yield was positively correlated to N and K efficiency, plant height, leaf and stem weight, stem girth, mean weight of tubers, number of nodes, girth and length of tubers, while negatively correlated to tuber starch and dry matter content. Path analysis showed that tuber length gave highest positive direct effect on yield followed by number of tubers, number of leaves, tuber starch content, plant height and nitrogen efficiency. Diversity studies grouped the genotypes into eleven clusters and the characters that gave the maximum contribution to divergence were tuber dry matter content, N and K efficiency. Root studies on thirty genotypes revealed that root traits like number of nodal roots, basal roots, adventitious roots, storage roots and root length displayed significant positive correlations with N and K efficiency. Evaluation of five highly nutrient efficient genotypes at the three levels of fertilizers (0%, 25% and 50% of the recommended dose of fertilizers) showed overall significance for traits like plant height, the number of leaves retained, stem weight per plant, girth of the stem, tuber yield, length of tuber, stem K content, tuber K content, total N and K uptake, N and K efficiency. The highest yielder was KBH 18 followed by 8S501-2. Maximum N efficiency was observed for KBH18 followed by 15S409, while maximum K efficiency was recorded for 8S501-2 followed by 15S409. Results showed that from 0 to 25 % there is an escalation in tuber yield as well as N and K efficiency, while the values at 25 and 50% are on par. All the selected four genotypes showed significant superiority over the K efficient check variety – Sree Pavithra – in terms of tuber yield, N efficiency and K efficiency. The study identified nine nutrient responsive genes in cassava which includes NRT1, NRT3, NLP1, GPT2, AMT1, TAR2 for nitrogen and KUP3, KUP4, KUP8 for potassium. Expression studies done using these genes in contrasting genotypes for N and K efficiency raised under field conditions showed significant upregulations and downregulations in their expression for efficient and less efficient genotypes. Allele mining for allelic variations in contrasting genotypes (15S409 and Export kappa) for two genes (AMT2 and NTR3) didn’t show much significant variation. Although SNP differences were observed for NRT3 gene, further functional studies are required to confirm this result. The study identified three main nutrient efficient genotypes viz., KBH18, which was the highest yielder, highest in N efficiency and third highest in K efficiency, 8S501-2, which was second highest in yield, highest in K efficiency, third highest in N efficiency and also exhibited early bulking and 15S409, which was the third highest yielder, second highest in N efficiency & K efficiency. The superior genotypes identified in the present study can be subjected to field trials for confirming their superiority and release as a variety.ThesisItem Open Access Variability in horsegram(macrotyloma uniform(Lam) verdc): under open and partially shaded conditions(Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2019) Swathy Sivan; KAU; Arya, KThe present study entitled “Variability in horsegram [Macrotyloma uniflorum (Lam.) Verdc.] under open and partially shaded conditions” was carried out in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani during 2017-2019. The study was undertaken to assess the variability and performance of horsegram genotypes collected from different regions under open and partially shaded conditions, for yield and protein content. Thirty genotypes of horsegram were collected from different regions of state and outside and were raised under open and partially shaded conditions, simultaneously for variability analysis. The partial shade was provided by coconut garden, planted at a spacing of 7.8 x 7.8 m, where the average shade percent was 24. These accessions were evaluated in a Randomized Block Design (RBD) with three replications during September 2018 to February 2019. Analysis of variance revealed significant difference among the genotypes for all the fifteen characters studied. Pooled analysis was also conducted for all the characters to compare the performance of genotypes under open and partially shaded conditions. The genotypes exhibited significant difference for characters such as number of primary branches plant-1, days to 50% flowering, days to maturity, number of pods plant-1, harvest index, crop duration and seed yield plant-1 under the two conditions. Under both conditions, genotypic coefficient of variation (GCV) was high for seed yield plant-1 and number of pods plant-1 while, characters like primary branches plant-1, secondary branches plant-1, pods plant-1, seed yield and harvest index exhibited high values for phenotypic coefficient of variation (PCV). High heritability coupled with high genetic advance was observed for seed yield plant-1, days to sprouting, days to 50% flowering, nodes plant-1, pods plant-1 and plant height under both conditions whereas, under partially shaded conditions, two more characters such as primary branches plant-1 and harvest index also showed high heritability with high genetic gain. Seed yield plant-1 was found to be significantly and positively correlated with number of primary branches plant-1, number of secondary branches plant-1, nodes plant-1, pods plant-1, seeds pod-1 and 100-seed weight both at genotypic and phenotypic levels under open and partially shaded conditions. An improvement in these characters would lead to an enhancement in the seed yield plant-1. Path analysis was carried out using seed yield plant-1 as the dependent character and other characters as independent variables. It revealed that number of pods plant-1, seeds pod-1, nodes plant-1, 100-seed weight, days to maturity and number of primary branches plant-1 were the primary yield contributing characters due to their high direct effect on seed yield plant-1. Genetic divergence was studied under open conditions using Mahalanobis’ D2 statistics and based on this analysis, the thirty genotypes were grouped into eight clusters. The maximum number of genotypes were accommodated in Cluster I (12), followed by Cluster II (6), Cluster III (5), Cluster IV & Cluster V with two genotypes each and Clusters VI, VII and VIII were solitary. Among the eight clusters, the highest inter cluster distance was recorded between Clusters V and VIII, while Cluster V also exhibited maximum intra cluster distance. It was observed that among the individual traits, seed yield plant-1 contributed highest for divergence followed by primary branches plant-1 and days to maturity. The results of the study revealed the presence of wide variability among the thirty horsegram genotypes under open and partially shaded conditions. The genotype T12 (Palakkad local) was found to be superior in yield performance both under open (20.08 g) and partially shaded conditions (18.36g), followed by the genotype T2 (Chintada local) from Andhra Pradesh (19.82g, 17.75g). Also the genotype T21 (IC22762) (18.22g) was found to be a high yielder under open conditions and genotype T17 (Attapadi local) (16.99g) under partially shaded conditions. When protein content was assessed, maximum value (28.92%) was recorded for genotype T14 (Dharmapuri local) under open conditions and genotype T23 (IC15735) (29.17%) under partially shaded conditions. The superior genotypes identified in the present study can be utilized for further crop improvement programmes to develop high yielding varieties.
