Developing germplasms and genetic analysis of strong ratooning ability in <italic>indica</italic> rice

Abstract

Ratooning rice can efficiently utilize temperature and heat resources from the sun to increase multiple cropping index and grain yield while benefiting from one sowing and two harvests. Therefore, it is very important to rice production and food security in China. The high-yield germplasms of ratoon rice are the material basis for breeding varieties with strong ratooning ability. The lack of rice varieties with robust ratooning ability is a key factor restricting the development of ratoon rice. At present, the germplasm with strong ratooning ability is lack, and ratoon rice varieties are mainly selected from the varieties popularized in production. Therefore, it is important to apply direct breeding strategies to select for varieties of ratoon rice. The breeding technology of ratooning rice is continuously improving, and there are two methods to breed new varieties of ratoon rice. One approach is to employ combining ability to select for elite parents with strong ratooning ability and estimate the heritability of ratooning ability, which can be used to decide on selecting varieties or combinations with strong ratooning ability from its offspring. The second approach is to screen for characteristics closely related to ratooning ability of the 1st season rice. With the improvement of breeding technology, researching and solving the problem of rice ratooning ability from pedigree breeding and genetic effects will provide technical support and guarantee the direct breeding of new rice varieties with ratooning abilities. Using eight restorers applied in a large area of production as materials, directional selection and germplasm innovation were carried out by the pedigree method. In order to study the genetic characteristics of ratooning ability, the ratio of stems of ratooning bud to total stems were analyzed in a 4×4 incomplete diallel design by using the additive-dominant model. The results showed the following: (1) Genetic expression of ratooning ability was mainly controlled by both additive and dominant effects, but they were easily influenced by environmental conditions and cultivation techniques. (2) Predicted value of heritability of the ratooning ability traits were significant or extremely significant, and broad heritability ( h 2 B ) was significantly higher than broad heritability ( h 2 N ). (3) The ratooning ability was significantly different among rice restoring lines, and the ratooning ability traits of the restoring lines, Minhui 3301 and Yahui 627 had significant positive additive effects and negative dominant effects, which were suitable for screening parents with strong regeneration ability. (4) The new germplasm resources of Ra201, Ra202 and Ra212 had a higher ratio of stems of ratooning buds to total stems and strong ratooning ability, among which Ra202 had obvious advantages of low-node germination and could be used as parents for the gene mining and utilization of the ratooning ability in indica rice. (5) The study on breeding methods of ratoon rice cultivars has further improved the classical breeding techniques, and has the advantages of indirect identification and early screening. The effect of new germplasm creations and new breeding varieties were useful and insightful.