A comprehensive understanding of CMS/Rf system enabled by modern omics tools and technologies considerably improves our ability to harness hybrid technology for enhancing the productivity of field crops.
 Harnessing hybrid vigor or heterosis is a promising approach to tackle the current challenge of sustaining enhanced yield gains of field crops. In the context, cytoplasmic male sterility (CMS) owing to its heritable nature to manifest non-functional male gametophyte remains a cost-effective system to promote efficient hybrid seed production. The phenomenon of CMS stems from a complex interplay between maternally-inherited (mitochondrion) and bi-parental (nucleus) genomic elements. In recent years, attempts aimed to comprehend the sterility-inducing factors (orfs) and corresponding fertility determinants (Rf) in plants have greatly increased our access to candidate genomic segments and the cloned genes. To this end, novel insights obtained by applying state-of-the-art omics platforms have substantially enriched our understanding of cytoplasmic-nuclear communication. Concomitantly, molecular tools including DNA markers have been implicated in crop hybrid breeding in order to greatly expedite the progress. Here, we review the status of diverse sterility-inducing cytoplasms and associated Rf factors reported across different field crops along with exploring opportunities for integrating modern omics tools with CMS-based hybrid breeding.

Cytoplasmic male sterility (CMS) in hybrid breeding in field crops

Sorghum (Sorghum bicolor) is one of the major cereal
crops consumed in India after rice (Oryza sativa) and
wheat (Triticum aestivum). The crop is primarily
produced in Maharashtra and southern states of
Karnataka and Andhra Pradesh. These three states
together account for close to 80% of the all-India
production. Madhya Pradesh, Gujarat and Rajasthan are
the other states producing sorghum. India is the third
largest producer of sorghum in the world with 7.15
million tons during 2007 and almost entire production of
sorghum (95%) in the country comes from the above
regions/states (GOI 2007).

An analysis of availability and utilization of sorghum grain in India

Sorghum has great potential as an annual energy crop. While primarily grown for its grain, sorghum can also be grown for animal feed and sugar. Sorghum is morphologically diverse, with grain sorghum being of relatively short stature and grown for grain, while forage and sweet sorghums are tall and grown primarily for their biomass. Under water-limited conditions sorghum is reliably more productive than corn. While a relatively minor crop in the United States (about 2% of planted cropland), sorghum is important in Africa and parts of Asia. While sorghum is a relatively efficient user of water, it biomass potential is limited by available moisture. The following exhaustive literature review of sorghum production practices was developed by researchers at Oak Ridge National Laboratory to document the current state of knowledge regarding sorghum production and, based on this, suggest areas of research needed to develop sorghum as a commercial bioenergy feedstock. This work began as part of the China Biofuels Project sponsored by the DOE Energy Efficiency and Renewable Energy Program to communicate technical information regarding bioenergy feedstocks to government and industry partners in China, but will be utilized in a variety of programs in which evaluation of sorghum for bioenergy ismore » needed. This report can also be used as a basis for data (yield, water use, etc.) for US and international bioenergy feedstock supply modeling efforts.« less

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Review of Sorghum Production Practices: Applications for Bioenergy

Sorghum acts as a dietary staple for millions of people living in about 30 countries in the subtropical and semi-arid regions of Africa and Asia. It is a source of food and fodder, mostly in the traditional, smallholder farming sector. It also finds a place in the high-input commercial farming sector as a feed crop, and is fast emerging as a biofuel crop. More than 80 % of the global sorghum area is characterized by low yield levels contributing to slightly above half of total grain output whereas the rest comes from the developed world with high yield levels. Though sorghum cultivation is reported from more than 100 countries, only eight countries have over 1 million ha area under sorghum, which together contribute more than 60 % of world sorghum production. In Africa, although only a few countries contribute a major share of area, sorghum is widely distributed and is a major staple food grain in large parts of the continent. In spite of its economic importance, sorghum cropped area around the world has declined over the last four decades at a rate of over 0.15 million ha per year. However, in some countries including Brazil, Ethiopia, Sudan, Australia, Mexico, Nigeria, and Burkina Faso it is expanding, mainly because of new land brought under sorghum cultivation or diversion of a portion of area planted to other crops such as maize and wheat. Global sorghum production peaked during the mid-1980s, and thereafter it declined by about 13–15 %, but not steadily. In almost all the sorghum growing regions except Africa yield levels have been enhanced over the years as a result of improved cultivars, higher input use, better resources, and crop management. Most of the sorghum is consumed in the countries where it is produced and world trade is mainly linked to demand for livestock products, which is governed by the feed requirements and prices in developed countries. Consumption of sorghum for food purposes is declining because of a change in food habits and consumer preference brought about by economic status, whereas use for animal feed and other industrial purposes is increasing. Under a changing climate regime sorghum would assume renewed importance as a food and industrial crop, and therefore concerted focus is necessary on such marginalized crops to ensure food and nutritional security in a sustainable manner in the years to come.

Economic Importance of Sorghum

Perennial grain crops have been proposed as a transformative approach to agriculture. Replacing annual staple crops with perennialized growth types of the same crops could provide environmental services, improve labour efficiency and weather resilience, reduce seed costs and produce livestock fodder or fuelwood production. Yet, the technologies and science for agricultural development in Africa have focused almost exclusively on annuals. In this paper, we review the literature to explore what has been potentially overlooked, including missed opportunities as well as the disadvantages associated with perennial grains. The case studies of pigeon pea and sorghum are considered, as an analogue for perennial grain crops in Africa. We find that a substantial number of farmers persist in ‘perennializing’ pigeon pea systems through ratoon management, and that sorghum ratoons are widely practiced in some regions. In contrast, many crop scientists are not interested in perennial traits or ratoon management, citing the potential of perennials to harbour disease, and modest yield potential. Indeed, an overriding prioritization of high grain yield response to fertilizer, and not including accessory products such as fodder or soil fertility, has led to multipurpose, perennial life forms being overlooked. Agronomists are encouraged to consider a wide range of indicators of performance for a sustainable approach to agriculture, one that includes management for diversity in crop growth habits.

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Perennial grains for africa: possibility or pipedream?

Sorghum (Sorghum bicolor L. Moench) is the first self-pollinated cereal staple crop, wherein heterosis has been commercially exploited to improve its productivity. Although the heterosis was demonstrated as early as 1927 in
sorghum (Conner and Karper 1927), its commercial exploitation was possible only after the discovery of a stable and heritable cytoplasmic-nuclear male-sterility (CMS) mechanism (Stephens and Holland 1954). This CMS system has been designated as A1 (milo). Since then a large number of hybrids have been developed and released/marketed for commercial cultivation in Asia, the Americas, Australia and Africa. The hybrids have contributed significantly to
increased grain and forage yields in several countries. The grain productivity increased by 47% in China and by 50% in
India from the 1960s to the 1990s (FAO 1960–1996), which corresponds well with the adoption of hybrids in these
countries. Adoption of the first commercial hybrid (CSH 1) in India over much of the rainy season sorghum area, while
local varieties are confined to fairly narrow specific environmental niches stands testimony to the wide adaptability of hybrids over varieties (House et al. 1997). Currently, over 95% of the sorghum area is planted to the hybrids in USA, Australia and China. In India, over 85% of the rainy season sorghum area is planted to hybrids.

Sorghum Hybrid Parents Research at ICRISAT–Strategies, Status, and Impacts

Sorghum [Sorghum bicolor (L.) Moench] is the first ever self-pollinated cereal staple crop in which heterosis has been commercially exploited using a cytoplasmic-nuclear male-sterility (CMS) mechanism to improve productivity. This system was first described in sorghum by Stephens and Holland (1954). This CMS system has been designated as A1 (milo). Since then a large number of hybrids have been developed and released and/or marketed for commercial cultivation in all sorghum-growing countries with a strong national agricultural research system (NARS). These hybrids have contributed significantly to increasing grain and forage yields in several countries. Encouraged by this success, continued research investments have been made in the development of hybrid parents [male-sterile (A-) lines (seed parents) and restorer (R-) lines] and hybrids by the sorghum improvement programs of several NARS and by ICRISAT. Research on hybrid parents at ICRISAT was initiated in 1978 at its headquarters at Patancheru, Andhra Pradesh, India; in 1985 at Bulawayo, Zimbabwe in Eastern and Southern Africa; and in 1982 at Sotuba, Mali in Western and Central Africa. In this article, we review the progress made in hybrid parents research in the light of strategies followed, and sketch the outline of future research at ICRISAT.

http://ejournal.icrisat.org/cropimprovement/v2i1/v2i1sorghumhybrid.pdf

Mary Mgonja

Papers

Sorghum Hybrid Parents Research at ICRISAT–Strategies, Status, and Impacts

Sorghum Hybrid Parents Research at ICRISAT: Retrospect and Prospects