VARIABILITY IN RICE BLAST PATHOGEN (Pyricularia oryzae B.C. Couch) AND MOLECULAR PROFILING OF BLAST RESISTANCE GENES IN RICE GENOTYPES
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Date
2023-12-26
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Acharya N G Ranga Agricultural University
Abstract
The present investigation was undertaken with an aim to know the variability between leaf blast and neck blast pathogen populations. Studies carried out on the variability of isolates using morphological and molecular characteristics. In another study efforts were made to identify the blast resistance genes in rice genotypes.
Survey was conducted during rabi, 2021-22 in five different mandals of West Godavari district of Andhra Pradesh for the collection of blast diseased samples and to assess the severity of the disease. The highest mean leaf blast Per cent Disease Index (PDI) 38.48% was recorded in Bhimadolu mandal and the lowest was recorded in Palakollu mandal (18.31%). Among the five mandals, highest neck blast incidence was recorded in Bhimadolu (8.74%).
A total of 10 monoconidial isolates of Pyricularia oryzae were established. Out of ten isolates, five were leaf blast (WLB-1 to WLB-5) and five were neck blast isolates (WNB-1 to WNB-5.)
The variability in radial growth, colony colour, growth pattern, elevation was studied among the isolates of P. oryzae. Variation existed among the isolates in their conidial dimensions. The longest conidia were observed in the isolate WNB-4 (24.44±0.90) and the shortest conidia in the isolate WLB-1 (18.04±1.58). The broadest conidia were observed in WNB-4 (8.50±1.06) and the narrowest in WNB-5 (6.70±0.96).
Molecular identification of P. oryzae isolates with ITS4 and ITS5 universal primers were used in order to support the morphological identification of P. oryzae isolates. All the isolates were appeared as identical by producing the amplified fragment of 560 bp. These results further confirmed the identification of the isolates as P. oryzae. The genetic diversity of P. oryzae isolates was studied using a total of 5 SSR markers. The PIC values ranged from 0.68 to 0.84 with average of 0.78 per marker. The SSR analysis formed two main clusters (I–II) at the Dice similarity coefficient of 0.63. This grouping revealed that, all the isolates were clustered in accordance of leaf blast and neck blast isolates, but not in the specificity of geographical location.
A set of 48 genotypes were screened against leaf blast and neck blast during rabi, 2021-22. The same set of genotypes were also profiled for blast resistance genes by using 10 SSR markers. From the phenotypic data 14 genotypes were found as resistant genotypes for both diseases. Eight genotypes viz., LRP 276, Pusa 1882-12-111-7, Pusa Basmati -1, Pusa 1886-13-91-26-9, CR 4156-1-506-2-24, RYT 3437, NLR 20104 and NLR 145 with major R genes i.e., Pi1, Pi2, Pi54, Pita and Pikh combinations were identified as promising lines for rice blast resistance.