BREEDING FORAGE CROPS FOR IMPROVED ABIOTIC STRESS TOLERANCE-A REVIEW
J. S. VERMA*
Department of Genetics and Plant Breeding
G. B. Pant University of Agriculture & Technology, Pantnagar-263 145, India
*(e-mail : email@example.com)
(Received: 25 February 2019; Accepted: 3 May 2019)
Forage crop production is largely limited by abiotic stress such as drought, salinity, temperature and other edaphic stresses because most forages are grown in marginal agricultural lands that have even poorer soil and land management system featured with low water holding capacity, infrequent irrigation, limited fertility or high salt content. Conventional and genetic engineering approaches have been used to improve stress tolerance of forage grasses and legumes. Modern conventional plant breeding is undergoing revolutionary changes that embrace new marker technologies and more profound understanding of the mechanisms that constitute complex traits. Traditionally, major gene and polygenic variation has been analyzed in different ways, but the use of new DNA markers and techniques of QTL analysis now allow to more integrated approaches in dissecting complex traits and assessing gene effects. Useful information on the genetic basis of abiotic stress tolerance has been obtained by moving genes between plants of the same or closely related species. Gene introgression achieved by conventional cross pollination means that created a range of genetic variation available to understand and manipulate genetic adaptation to environmental change is greatly enhanced. Drought and cold tolerance has been improved within the Lolium / Festuca species complex. A link was found between drought tolerance and enhanced deeper root growth under water limiting conditions in tall fescue and alfalfa. The differences in the level of freezing tolerance between non-hardy and hardy alfalfa cultivars was found to be related to the capacity of the plants to accumulate raffinose and stachyose in their roots and crowns other than the capacity to accumulate sucrose earlier than non-dormant plants. Proline content in alfalfa leaves and roots increased dramatically when plants were subjected to drought and two genes controlling the transcriptional regulation of key proline cycle enzymes in alfalfa have been identified and cloned. Wide hybridization with relative species followed by chromosome and / or chromosome fragment introgression has been considered an efficient way to transfer drought, salt and other stress tolerance gene(s) to the target species to widen the gene pool. Intergeneric hybrids between Lolium (Ryegrass) and Festuca (Fescue) species have received much attention by forage breeders. Enhanced drought tolerance in cowpea is accompanied with (i) better water- use efficiency and tolerance to water –deficiency and extreme heat conditions, (ii) better recovery of plants after drought is removed i.e., on re-watering. Both types of drought tolerance are dominant traits controlled by a single dominant gene Rds1 and Rds2 respectively. In white clover drought tolerance improvement programme, introgression has also been used as a route to transfer the morphological or physiological traits from its related wild species that show more drought tolerance or have better persistence. Endophyte-infected grasses are better adapted than non-infected grasses to abiotic stresses i.e., drought and marginal soil conditions due to direct changes affecting water status in shoots and indirect changes in root morphology and function.
Key words: Abiotic stress, tolerance, forage crops, breeding, intergeneric hybridization, endophyte