ABSTRACT Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is one of the major hindrances in rice (Oryza sativa L.) production across the world including Malaysia. Therefore, the development of disease-resistant varieties remains a very economical and effective method of controlling BLB in rice. Based on this background, this study was conducted to analyze segregation pattern of simple-sequence repeat (SSR) markers associated with BLB resistance genes in an F2 bulk population derived from a resistant variety (IRBB60) and a susceptible variety (MR219). Out of 129 simple sequence repeat (SSR) markers screened, 18 distinct polymorphism markers including R-gene based markers were used to screen 345 F2 progenies for resistance to BLB. Among the polymorphic markers, the chi-square analyses showed that 15 SSR markers (i.e. RM13 (xa5), RM21 (Xa21), RM122 (xa5), RM153 (xa5), RM164 (Xa13), RM206 (Xa10), RM5509, RM20B, RM25, RM163, RM169, RM218, RM267, RM276, and RM334) had a segregation ratio of 1:2:1 for a single gene model (df = 2.0, p ≤ 0.05). For phenotypic ratio, the F2 population segregated in ratio 3:1 (R:S) for resistant and susceptible plants, respectively. This indicated that resistance to BLB caused by pathotype X. oryzae pv. oryzae (Xoo) in the ‘MR219’ × ‘IRBB60’ F2 population is controlled by single dominant genes. The result presented in this study will help breeders to further breeding research in rice by enabling selection based on the genotype rather than on the phenotype. Similarly, the markers reported in this study will serve as a valuable tool for marker-aided selection for BLB resistance gene.

RESUMOO estudo foi realizado no Centro de Arroz da Universidade Putra Malásia (UPM), para avaliar o desempenho produtivo de plantas resistentes a brunose do arroz recém desenvolvidas de BC2F3 gerações derivadas do cruzamento entre MR263, uma variedade de arroz de alta produtividade, embora suscetível a brunose e Ponsu Seribu 1, doador com resistência a brunose [Pi- 7 (t) e Pi-d (t) 1, Pir2-3 (t)genes e qLN2 QTL], e também uma variedade local da Malásia. Com base nas características avaliadas, as plantas 12, 6, 7, 5, 21, 22, 5, 26, 11, 8, 10, 13 e 15 apresentaram o maior rendimento, resistência a brunose e boas características morfológicas. Mais de 70% de herdabilidade foram encontradas em dias para maturação, altura da planta, número de perfilhos por cova, e panículas por cova, 80% de herdabilidade foram encontradas em grãos e rendimento por colina e mais de 90% de herdabilidade foi observada em grãos, largura de grãos e peso das sementes. A análise de agrupamento com base nos traços agruparam 30 plantas, juntamente com MR263 em sete clusters. De acordo com o PCA, os quatro primeiros componentes principais responsáveis por cerca de 69,3% da variação total para todas as características medidas apresentaram alta correlação entre as características analisadas.

ABSTRACTThe study was carried out in the University Putra Malaysia (UPM) Rice Research Centre to evaluate the yield performance of newly developed selected blast resistant plants of BC2F3 generations derived from a cross between MR263, a high yielding rice variety but blast susceptible and Pongsu Seribu 1, donor with blast resistant (Pi-7(t)and Pi-d (t)1, Pir2-3(t)genes and qLN2 QTL), Malaysian local variety. On the basis of assessed traits, the plants 12, 6, 7, 5, 21, 22, 5, 26, 11, 8, 10, 13 and 15 had the higher yield, blast resistant and good morphological traits. More than 70% heritability was found in days to maturity, plant height, tiller numbers per hill, and panicle per hill, 80% heritability was found in filled grain and yield per hill and more than 90% heritability was found in grain length, grain width and seed weight. Cluster analysis based on the traits grouped 30 plants along with MR263 into seven clusters. According to PCA, the first four principal components account for about 69.3% total variation for all measured traits and exhibited high correlation among the characteristics analyzed.

Genetic variability with mutagenic agents has been employed in plant breeding due to its significant contribution to the improvement of the existing rice genotypes by using genetically diverse parents. This study evaluated the genetic variability and diversity of mutant rice using quantitative traits and inter-simple sequence repeats (ISSR) molecular markers. A field experiment was carried out on M5 generation of 31 developed mutant lines and their parent (control). Morphological traits and 25 ISSR molecular markers were used as tools for determining cultivar identities and genetic diversity. The selected primers generated 443 clear polymorphic bands with an average number of 18 per primer. The bands were 85.10 % polymorphic. Un-weighted Pair Group of Arithmetic Means (UPGMA) with similarity coefficients were used for cluster analysis. Through this, all the genotypes were grouped into six clusters. It was shown that crosses between MR219-ML8 and MR219-ML22 could be done for development of high yielding varieties. Also, these mutants could be used as donor parents in rice breeding programs and some can be recommended as new rice varieties suitable for rice cultivation in Malaysia.

La variabilidad genética con agentes mutagénicos se ha usada en el cultivo de plantas debido a su contribución significativa a la mejora de los genotipos existentes de arroz a través de padres genéticamente diversos. En este estudio se evalúo la variabilidad y diversidad de mutantes de arroz mediante rasgos cuantitativos y marcadores moleculares de inter-secuencias simples repetidas (ISSR). El estudio se realizó en campo, en la generación M5 de 31 líneas mutantes desarrolladas y su padre (testigo). Características morfológicas y 25 marcadores ISSR se utilizaron como herramientas para determinar las identidades y diversidad genética de los cultivares. Los iniciadores seleccionados generaron claras 443 bandas polimórficas claras con un número promedio de 18 bandas por iniciador. Las bandas fueron 85.10 % polimórficas. El método no ponderado de pares de grupo de medias aritméticas (UPGMA) con coeficientes de similitud se usó para el análisis de los grupos. Mediante esto, todos los genotipos se agruparon en seis grupos. Las cruzas entre MR219-ML8 y MR219-ML22 podrían generarse para desarrollar variedades de alto rendimiento. Además, estos mutantes se pueden usar como padres donadores en programas de mejoramiento de arroz y algunos pueden recomendarse como variedades nuevas de arroz adecuadas para su cultivo en Malasia.