Screening Amaranthus (Amaranthus spp.) genotypes for yield, quality and Rhizoctonia leaf blight

Abstract

Amaranthus (Amaranthus spp.) is a nutrient rich leafy vegetable grown in tropical and subtropical regions, especially in Southern India. It is valued as an excellent source of proteins, vitamins, dietary fiber, minerals, and bioactive compounds with antioxidant and therapeutic properties. Amaranthus is commonly referred to as the “poor man’s spinach” because of its quick growth habit, superior nutritional value, and low cultivation cost. As a C₄ photosynthetic plant, amaranthus thrives well under adverse climatic conditions, produces high yields, and serves as an ideal component of sustainable agriculture. It shows a wide range of variability for morphological and quality characters highlighting its potential for effective genetic improvement. Leaf blight disease caused by the soil borne fungal pathogen Rhizoctonia solani Kühn poses a major challenge to amaranthus cultivation. It severely reduces the crop’s yield potential and overall market quality. The disease initially appears as small, irregular creamy white spots on the leaves, which expand under humid conditions to form large translucent and light green lesions, ultimately leading to the development of shot hole symptoms. The use of chemical fungicides for the control of disease is not advisable especially for leafy vegetables due to the risk of pesticide residue accumulation. Development of resistant varieties stands out as the most efficient method for the management of the disease. The present study entitled “Screening amaranthus (Amaranthus spp.) genotypes for yield, quality and resistance to Rhizoctonia leaf blight” was undertaken at the AICRP on Vegetable Crops, College of Agriculture, Vellanikkara from 2024 to 2025 to assess the genotypes for yield and quality traits and to screen them for Rhizoctonia leaf blight. In the first experiment, forty five diverse amaranthus genotypes were evaluated in a Randomized Block Design with two replications for yield, quality and Rhizoctonia leaf blight tolerance. Substantial variability was observed in morphological, biometric, disease reaction and biochemical traits. The morphological characterization of forty five amaranthus genotypes revealed variability across majority of the recorded traits. Among the genotypes, VLKAM-42 recorded the highest yield per plant followed by VLKAM-37. Three genotypes viz., VLKAM-25, VLKAM-41 and VLKAM-42 were completely free from the Rhizoctonia leaf blight under field conditions and recorded a zero disease index (PDI) value. The genotype VLKAM-36 displayed a very low PDI (6.44) and was classified as highly resistant. High genotypic and phenotypic coefficients of variation were exhibited by the traits such as plant height, stem girth, leaf length. leaf width, petiole length, number of branches, leaf weight, stem weight, yield per plant, beta carotene, chlorophyll, carotenoid, oxalate and nitrate content. High heritability coupled with high genetic advance was recorded in most of the biometric and biochemical characters, indicating that the inheritance of these characters is mainly governed by additive gene effects. Hierarchical cluster analysis grouped the forty five genotypes into seven distinct clusters, reflecting broad genetic diversity among them. Significant positive correlations were observed between yield per plant and characters such as stem weight, leaf weight, stem girth, plant height, leaf length, petiole length and leaf width. In the second experiment, ten genotypes showing immune to moderate resistance in the field were screened in-vitro with artificial inoculation of Rhizoctonia solani. The accession VLKAM-41 remained free of symptoms. The accessions VLKAM-25, VLKAM- 36, and VLKAM-42 showed only limited lesion development. The genotypes VLKAM-34, VLKAM- 14, VLKAM-10 and VLKAM- 24 exhibited small lesions with limited expansion indicating a moderately resistant reaction. A multiple trait selection index integrating key quantitative, biochemical and disease resistance parameters, ranked VLKAM-42 as the best performing genotype followed by VLKAM-37, VLKAM-41, VLKAM-43 and VLKAM-40. These genotypes possess a combination of good yield performance, favourable biochemical traits, and disease resistance, making them promising candidates for future breeding efforts. The present study revealed a wide range of morphological and genetic variability among the amaranthus genotypes. It also identified amaranthus genotypes with stable resistance to Rhizoctonia leaf blight which can be used as valuable donor sources in the future breeding programmes for the development of leaf blight resistant varieties