Morphological characterization of rice germplasm for rice grain discoloration resistance

Abstract

Adnan Shakir, Muhammad Ashfaq*, Muhammad Arshad Javed, Hafiz Muhammad Bilal, Mehwish Jabeen, Muhammad Ali, Muhammad Muneeb Hashmi, Qurban Ali, Muhammad Jamil

Rice grain discoloration is a complex disorder which occurs due to the infection of various microorganism(s) on glumes/kernels or both. A study was conducted on the discoloration of existing rice germplasm and potential sources for resistance to be utilized in future breeding programs. 200 rice lines (land races, approved varieties and advanced breeding lines) were collected from Plant Genetic Resources Institute (PGRI), National Agricultural Research Centre (NARC) Islamabad Pakistan; Rice Research Institute (RRI) at Kala Shah Kaku, Pakistan; International Rice Research Institute (IRRI), Philippines; China National Rice Research Institute (CNRRI), China and United States Department of Agriculture, United States of America. Rice germplasm were sown at Rice Research Institute (RRI), Kala Shah Kaku and tested in terms of their phenotype expression. The experiment was designed in a three replicated Alpha Lattice Design (ALD). Throughout the season the standard agronomic practices were followed as recommended by Punjab, Pakistan for transplanting (30 days after sowing), recommended dose of Nitrogen, Phosphorus, and Potassium (NPK) fertilizer (25:35:55 kg acre-1) and irrigation management. The results indicated that there was a large phenotypic variation between the cultivars with Coefficient of Variation expressed as a percentage (CV%) ranging from 1.32 (days to maturity) to 54.7 (unfilled grains per panicle). Plant height ranged from 80.0 to 189.3 cm. Number of tillers per plant ranged from 13.3 to 48.7 with an average of 24.9 (Coefficient of Variation (CV)=24.53%) and there was a slight skewness (1.41) due to the small proportion of lines with a very high number of tillers. For seed morphology (50 g seeds of each cultivar), seed length ranging from 7.05 to 11.95 mm mean=9.22 mm and CV=9.26% seed width from 1.68 to 3.60 mm mean=2.28 mm and CV=13.75% and length-to-width ratio from 2.24 to 6.22 (mean=4.13; CV=19.08%), spanning grain shape classes from medium to extra slender. The 1000 grain weight ranged from 11.27 to 28.29 g with a mean of 19.82 g CV=12.99% and n=199. The heritability estimates for traits with high Analysis of Variance (ANOVA) ranged from 1.68% for days to maturity to 100% for 1000-Grain Weight. seed length (h²bs=89.33%), seed width 89.20% and length-to-width ratio of 88.88% had highest heritability values followed by flag leaf area of 81.32% and unfilled grains per panicle of 79.98%. Approximately 3% to 78% of germplasm collection was confirmed to be resistant, moderately resistant, moderately susceptible and susceptible respectively with the disease incidence ranges being Percentage Disease Index (PDI) ≤ 12%, PDI 12-26%, PDI 26-50% and PDI>50%. The mean percentage of PDI was 34.87%, indicating that most of the lines were susceptible to disease under the pathogen pressure. Discoloration of the grain was observed in all germplasm panels ranging from less than 5% up to more than 70% with a mean PDI of about 34.87%. Level of resistant lines 7% and moderately resistant lines 27% indicate presence of natural resistance in cultivated Pakistani germplasm. The germplasm lines with grain quality were identified as candidates to be used in future breeding programs.