Dash Amit K, Rao Ravi N, Rao G J N, Verma Ram L, Katara Jawahar L, Mukherjee Arup K, Singh Onkar N, Bagchi Torit B
Biotechnology Laboratory, Crop Improvement Division, National Rice Research Institute, Cuttack India.
Front Plant Sci. 2016 Jul 13;7:1005. doi: 10.3389/fpls.2016.01005. eCollection 2016.
The cytoplasmic male sterile line system comprising CRMS 32A and its maintainer line CRMS 32B is a popular choice for the development of new hybrids in India as CRMS 32A, having Kalinga 1 cytoplasm (other than WA), is a viable alternative to WA cytoplasm. However, both lines are susceptible to bacterial blight (BB), a major disease on rice. As enhancement of host plant resistance is the most effective and economical strategy to control this disease, four resistance genes (Xa4, xa5, xa13, and Xa21) were transferred from a BB pyramid line of IR64, into the A and B lines using a marker-assisted backcrossing (MAB) breeding strategy. During the transfer of genes into CRMS 32B, foreground selection was applied using markers associated with the genes, and plants having resistance alleles of the donor, are selected. Selection for morphological and quality traits was practiced to select plants similar to the recurrent parent. The four gene and three gene pyramid lines exhibited high levels of resistance against the BB pathogen when challenged with eight virulent isolates. Using genome wide based SSR markers for background selection, pyramids having >95% of the recurrent parent genome were identified. With CRMS 32B gene pyramid as donor, the four resistance genes were transferred into the A line through repeated backcrosses and the A line pyramids also exhibited high level of resistance against BB. Through a combination of selection at phenotypic and molecular levels, four BB resistance genes were successfully introduced into two parental lines (CRMS 32 B and A) of Rajalaxmi, an elite popular hybrid. The pyramided B lines did exhibit high levels of resistance against BB. Selection for morphological and quality traits and background selection hastened the recovery of the recurrent parent genome in the recombinants. Through repeated backcrosses, all the four resistance genes were transferred to CRMS 32A and test crosses suggest that the maintenance ability of the improved CRMS 32B lines is intact. These improved maintainer and CMS lines can directly be used in hybrid rice breeding and the new hybrids can play an important role in sustainable rice production in India.
包含CRMS 32A及其保持系CRMS 32B的细胞质雄性不育系系统，是印度培育新型杂交种的常用选择，因为具有卡林加1细胞质（非WA）的CRMS 32A是WA细胞质的可行替代品。然而，这两个品系都易感染水稻的主要病害——白叶枯病（BB）。由于增强寄主植物抗性是控制这种病害最有效且经济的策略，利用标记辅助回交（MAB）育种策略，将来自IR64的一个白叶枯病基因聚合系的四个抗性基因（Xa4、xa5、xa13和Xa21）导入A系和B系。在将基因导入CRMS 32B的过程中，使用与这些基因相关的标记进行前景选择，选择具有供体抗性等位基因的植株。对形态和品质性状进行选择，以挑选出与轮回亲本相似的植株。当用8个强毒分离株进行挑战时，四基因和三基因聚合系对白叶枯病病原菌表现出高水平抗性。利用全基因组SSR标记进行背景选择，鉴定出具有>95%轮回亲本基因组的聚合系。以CRMS 32B基因聚合系为供体，通过反复回交将四个抗性基因导入A系，A系聚合系对白叶枯病也表现出高水平抗性。通过表型和分子水平的选择相结合，四个抗白叶枯病基因成功导入了优良杂交种拉贾拉克希米的两个亲本系（CRMS 32 B和A）。聚合的B系对白叶枯病确实表现出高水平抗性。对形态和品质性状的选择以及背景选择加速了重组体中轮回亲本基因组的恢复。通过反复回交，所有四个抗性基因都被转移到了CRMS 32A，测交表明改良后的CRMS 32B系的保持能力完好无损。这些改良的保持系和CMS系可直接用于杂交水稻育种，新的杂交种可在印度水稻可持续生产中发挥重要作用。
