Document Type : Research Paper
Authors
1
Agricultural and Horticultural Science Research Department, Khorasan Razavi Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization, Mashhad, 91769-83641, Iran.
2
Cotton research institute of Iran
10.22092/ijcr.2024.365051.1209
Abstract
Cotton, as a strategic crop and the most important fibre crop, is one of the most valuable agricultural crops that has a special economic, agricultural and commercial importance in the world and in Iran and has long been a subject for hybrid variety breeding. In this review, we have presented the latest advances in theoretical and applied research in the field of cotton heterosis and the methods used to develop hybrid varieties in recent decades. Three types of hybrids produced by manual emasculation, cytoplasmic male sterility and genetic male sterility have been developed and are being cultivated. The most desirable method of producing hybrid seed is to use the GMS or CMS line in combination with insect pollination when sufficient pollen is available to be pollinated by honey bees. The A and B lines can produce the same yield of seed cotton in the field. Currently, most hybrids grown commercially are produced by manual emasculation and pollination. Due to the high cost of producing F1 seed, F2 seed is therefore widely cultivated. The F2 generation of these combinations was 5 to 15 better in yield than the control varieties. One advantage of the F2 generation is that only half of the pollen of the F1 hybrid regains its fertility. However, the selection and certification of high heterosis in the F2 generation is necessary, as some F2 generations show no heterosis, although high heterosis is present in the F1 generation. In addition, there is heterosis in yield but not in fibre quality in F2. GMS genes (ms2 and ms5ms6) used in hybrid seed production and occasional mitochondrial genes for G. harknessii CMS were cloned. On the other hand, the discovery and improvement of environmental male sterility (EGMS), which is induced by environmental factors such as light and temperature, has enabled the utilisation of some GMS traits for hybrid breeding. The EGMS line can be used both as a sterile line and as a maintenance line by controlling the appropriate environment and realising the crossing of two lines. In this review, the challenges and opportunities of heterosis in cotton and the development of hybrid varieties are discussed.
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