Vimla Singh

Cultural and morphological variability among Rhizoctonia solani isolates from trans-gangetic plains of India

Banded leaf and sheath blight incited by Rhizoctonia solani f. sp. sasakii Khunn. (Teleomorph: Thanatephorus cucumeris) is gaining devastating potentials in India. The pathogen is reported to show variation in expression of symptoms on the same genotypes grown in different locations. Fifteen isolates from trans-gangetic plains of India were collected to examine the cultural and morphological variability and pathogenic behaviour on host Zea mays. The isolates were from maize and rice host origins. Considerable variability was found among the isolates. The isolates of maize origin were poor sclerotia producing in culture, formed compact dense/fluffy, pale white to yellowish growth on PDA, producing irregular to organized, smooth surfaced sclerotia, faster radial growth in culture, acute branching of hyphae and high pathogenicity. The rice isolates showed a contrasting behaviour in forming sub-central to scattered, pitted sclerotia lighter in weight than maize counterparts, compact sparse colony, slow to medium radial growth, light brown to dark brown colony. Aerial bearing was not recorded in most of these isolates. All the rice isolates were fast sclerotia initiating in culture; however, higher incubation period was recorded in pathogenicity tests. The lesions were also scattered and disease score ranged from 2.6–3.1. The cultural and morphological parameters used in this investigation may be used to examine the biology of R. solani isolates from other agro-climatic regions also.

Phytin: A Nutritional Inhibitor in Food and Feed - Review of Strategies and Challenges to Overcome the Menace in Maize

Maize (Zea mays L.) seeds forms an important ingredient of feed for poultry and swine and also a food for humans. In seeds stored phosphorus (P) largely occurs as phytin or Phytic acid (PA) a myo-inositol hexakisphosphate, Ins (1,2,3,4,5,6) P6, or InsP6. PA content is a major concern for nutritive value of maize. It is the storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 06 (2018) Journal homepage: http://www.ijcmas.com

Morphological and molecular variability among Indian isolates of Rhizoctonia solani causing banded leaf and sheath blight in maize

Rhizoctonia solani, a devastating soil borne fungus inciting banded leaf and sheath blight (BLSB) disease is a constraint in maize production and improvement program. Rhizoctonia isolates collected from seven diverse maize cropping zones of India were examined for morphological and molecular variability. All the tested isolates caused symptoms of BLSB on maize and were also cross infective on rice and sugarcane hosts, but showed significant variability in hyphal diameter, mean hyphal cell size, weight, size and distribution of scleorotia, culture pigmentation, incubation period, pathogenicity and expression of symptoms. Neighbour joining cluster analysis placed the 62 isolates of R. solani into four major groups, A, B, C and D. Group A was more diverse and included isolates of diverse agro-ecological zones. The cluster analysis corresponded well with principle component analysis. Pathogenicity testing of R. solani isolates on maize genotype (CM 501) revealed highly variable virulence pattern of the pathogen population suggesting its high evolutionary potential, and hence adaptability to diverse geographical regions. The study reveals a strong evidence of inherent potential of the R. solani isolates to survive in diverse ecological zones and its probable spread to other maize cultivars across India. Sequence comparisons of the internal transcribed sequence-ribosomal DNA region of 62 isolates did not reveal much diversity among the isolates. Majority of the isolates (n = 61) clustered together with anastomosis group (AG) AG1-IA used as reference strain in the phylogram, distinct from AG1-IB, AG2–2IIIB and Waitea circinata used as reference strains. BLSB isolates representing distinct geographical locations shared identical sequences indicating long-distance dispersal of the pathogen. The study confirms that the genetic flexibility of the pathogen allows for its adaptation to variable ecological niches and long-distance introduction of new genotypes into the region. The study emphasizes that epidemiological studies may complement the molecular studies.