RESUMEN
Sesbania sesban (L.) Merr., (family Fabaceae) commonly called as "dhaincha" in India, is a multi-purpose crop used as a cover crop, as green manure, in the paper industry as well as animal fodder. The leaves of Sesbania contain high amounts of pinitol, which acts as an anti-diabetic agent (Misra and Siddiqi 2004). During July/August from 2017 to 2019, Sesbania plants exhibiting typical Rhizoctonia-like symptoms, including collar rot, wilting, and necrotic lesions on stems were regularly observed at ICAR-Central Potato Research Institute Regional Station, Meerut, Uttar Pradesh. The disease incidence ranged between 5 and 10% in a Sesbania crop being grown on 25 ha in Sesbania-potato rotation. Ten diseased plants were collected from different fields and brought to the laboratory for diagnosis. Affected stem pieces approximately 5 mm in size were surface sterilized with 2% sodium hypochlorite, washed twice in sterilized water and air dried. Four diseased pieces per plate were inoculated on 2% water agar amended with 2% streptomycin sulfate and incubated at 28±1â in the dark. All four affected pieces began to produce Rhizoctonia-like colonies after 48 h of incubation and in total eight isolates were purified and stored at 4â for further use. The colonies of eight isolates were evaluated and all were whitish during early growth and became light brown after 72 h. Dark-brown sclerotia appeared in the random pattern on PDA after 120 h. Microscopic observations showed that all isolates had hyphal branching at right angles with slight constriction at the base of the branch, presence of dolipore septum near the branching and multinucleate individual hyphae compartments (Sneh 1991). Based on these morphological characteristics, the fungus was identified as Rhizoctonia solani. All isolates were further characterized to determine anastomosis group (AG) by pairing with a known AG tester of R. solani AG-1-IA (ITCC 7650), AG-1-IB (ITCC 5650), and AG-3 (RS-20) procured from Indian Type Culture Collection, Division of Plant Pathology, ICAR-Indian Agricultural Research Institute, New Delhi and ICAR-Central Potato Research Institute, Shimla, Himachal Pradesh, India, respectively. All eight isolates showed positive anastomosis with a known AG-1-IA tester isolate while no anastomosis was observed with other known tester isolates (Carling 1996). Furthermore, a single ~265 bp amplicon was amplified with AG-specific primer, which was specific to R. solani AG1-IA group; confirms the AG-specific identity of the isolates (Matsumoto 2002). Amplification was not observed with AG1-IB, AG3 and AG2 specific primers (Khodayari et al. 2009). The selected four isolates were molecularly characterized by amplifying the internal transcribed spacer (ITS) and ribosomal DNA (rDNA) 5.8s regions by polymerase chain reaction using ITS1 and ITS4 primer pairs (White et al. 1990). The nucleotide BLAST (BLASTn) analysis of the resulting four sequences i.e. GenBank acc. no. MT105386, MT105387, MT105388, and MT105389 supported the identification of the isolates as AG-1-IA sub-group and showed 95.12%, 98.93%, 96.79%, and 98.04%, respectively, sequence homology with known cultures of R. solani AG1-IA isolated from rice in China (KC285893), and India (MK481078). To confirm pathogenicity, Sesbania plants were grown in pots and maintained in the greenhouse at 25â with a 12-h-light/dark photoperiod. After 35 to 40 days of growth, the stems of ten Sesbania plant were artificially inoculated with PDA plugs containing R. solani mycelia (Jia et al. 2007) and covered with aluminium foil. Plants inoculated with noncolonized agar plugs served as control. After 96 h of incubation, all the plants inoculated presented the typical collar and stem rot symptoms. No symptoms were observed in the control plants. R. solani was re-isolated cent percent from these ten infected plants fulfilling Koch's postulates. R. solani AG1-IA has been reported to cause sheath blight and banded leaf and sheath blight diseases of rice and maize, respectively (Ogoshi 1987). To our knowledge, this is the first report of Sesbania sesban infected by R. solani AG1-IA, and serve as a host for the pathogen. The result from our findings will be helpful for planning of crop rotations in an agro-ecosystem.
RESUMEN
White mould or stem rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is a devastating fungal disease found in major potato cultivation areas worldwide. The aim of this study was to characterize genetic diversity in the S. sclerotiorum population from the main potato producing regions of India by means of morphological (mycelial growth, colony colour, number and distribution pattern of sclerotia) and molecular characteristics, as well as to evaluate the virulence of S. sclerotiorum isolates in potato for the first time. Among the S. sclerotiorum population analyzed, high phenotypic and genotypic diversity were observed. Using all the morphological characteristics, a dendrogram was constructed based on Gower's similarity coefficient that distributed all the isolates into three clusters at the 0.62 similarity coefficient. Carpogenic germination of apothecia revealed that larger sclerotia produced a greater number of apothecia while smaller sclerotia produced fewer apothecia. Pathogenicity test results revealed that out of 25 isolates, seven were highly aggressive, 14 were moderate and four had low aggressiveness, whilst isolates from Punjab were more pathogenic than those of Uttar Pradesh. Phylogenetic analysis of universal rice primer polymorphism showed high genetic variability within the isolates that grouped all the isolates in three evolutionary lineages in the resulting dendrogram and showed partial relationship with geographical locations of the isolates. Further, the findings suggest the occurrence of higher heterogeneity and genetic diversity among the S. sclerotiorum isolates that indicates the existence of both clonal and sexual reproduction in the pathogen population of potato producing areas in India.
Asunto(s)
Ascomicetos/clasificación , Ascomicetos/patogenicidad , Variación Genética , Enfermedades de las Plantas/microbiología , Solanum tuberosum/microbiología , Ascomicetos/genética , Evolución Molecular , India , Fenotipo , Filogenia , Filogeografía , Análisis de Secuencia de ADN , VirulenciaRESUMEN
In the present study, 95 isolates of bacteria were tested for their biosurfactant as well as biocontrol activity against Phytophthora infestans. The results revealed that only 15.8% isolates showed biosurfactant activity. The emulsification index ranged from 0-68% and 24.2% isolates showed positive reaction for biosurfactant properties. In emulsification assay and oil spreading test, 18.95% and 5.26% isolates, respectively scored positive for biosurfactant production. Among all, only five isolates were found effective against P. infestans, for biocontrol properties. Pseudomonas aeruginosa-1 showed 62.22% inhibition zone after 72 hrs while P. aeruginosa-3 showed 46.42%. Forty-eight hrs old culture supernatants were highly effective in food-poisoning test, tuber slice test and detached leaf method against P. infestans. In whole potato plant test, bacterial cell based formulation, culture supernatant and bacterial cell suspension of P. aeruginosa-1 showed 10.42%, 9.94% and 17.96% diseases severity respectively, as against 53.96% in control. This isolate holds promise as biological control agent against P. infestans in field.
Asunto(s)
Control Biológico de Vectores , Phytophthora infestans , Pseudomonas aeruginosa/aislamiento & purificación , Distribución Aleatoria , Solanum tuberosum , Tensoactivos/análisisRESUMEN
Potatoes are an important source of food for millions of people worldwide. Biotic stresses, notably late blight and potato cyst nematodes (PCN) pose a major threat to potato production worldwide, and knowledge of genes controlling these traits is limited. A genome-wide association mapping study was conducted to identify the genomic regulators controlling these biotic stresses, and the genomic prediction accuracy was worked out using the GBLUP model of genomic selection (GS) in a panel of 222 diverse potato accessions. The phenotype data on resistance to late blight and two PCN species (Globodera pallida and G. rostochiensis) were recorded for three and two consecutive years, respectively. The potato panel was genotyped using genotyping by sequencing (GBS), and 1,20,622 SNP markers were identified. A total of 7 SNP associations for late blight resistance, 9 and 11 for G. pallida and G. rostochiensis, respectively, were detected by additive and simplex dominance models of GWAS. The associated SNPs were distributed across the chromosomes, but most of the associations were found on chromosomes 5, 10 and 11, which have been earlier reported as the hotspots of disease-resistance genes. The GS prediction accuracy estimates were low to moderate for resistance to G. pallida (0.04-0.14) and G. rostochiensis (0.14-0.21), while late blight resistance showed a high prediction accuracy of 0.42-0.51. This study provides information on the complex genetic nature of these biotic stress traits in potatoes and putative SNP markers for resistance breeding.
RESUMEN
Currently, the multi-location testing of advanced hybrids in India is carried out at 25 centers under the All India Co-ordinated Research Project on Potato (AICRP-P), which is spread across the country. These centres have been chosen to represent different potato growing regions based on soil and agronomic features. However, the reliable deployment of the newly bred varieties in different regions requires a scientific delineation of potato growing zones with homogenous climates. The present study was undertaken to develop homogenous zones in the Indian sub-continent based on the environmental parameters of the potato growing season. A total of 1253 locations were identified across the country as having a plausible potato growing season of at least 70 days with suitable thermal limits. Six variables including five meteorological parameters including Physiological days (P days), Growing degree days (GDD), Mean daily temperature, Mean night temperature and Mean daily incident solar radiation, together with altitude as the sixth variable, were used for Agglomerative Hierarchical Clustering (AHC) and the Principal Component Analysis by Multidimensional Scaling (MDS) technique to derive identical classes. The thematic map of the classes was overlaid on potato growing districts of India using ArcGIS 9.1 software. The study clearly depicted that the clustering technique can effectively delineate the target population of environments (TPE) for potato genotypes performing well at different testing environments in India. The study also identifies target locations for future focus on breeding strategies, especially the high night temperature class having a large expanse in India. This is also vital in view of the impending climate change situation.