Abstract
Implementing appropriate breeding strategies for sunflower, alongside dependable information on heritability and gene effects upon yield and related traits under drought conditions, are all necessary. Thirty sunflower hybrids were produced by line × tester cross of six male-sterile and five restorer lines. Their hybrids were evaluated in three levels of irrigation, as follows: (1) non-stressed plots, irrigated at regular intervals (W1); (2) mild water stress (W2), irrigated from the beginning of the button stage (R4) to seed filling initiation (R6); (3) severe water stress (W3) started from the beginning of button stage (R4) to physiological maturity. Based on observations and specific methods for determination, canopy temperatures, chlorophyll index, relative water content and proline content, were studied by additive effects, under the different irrigation conditions. Canopy temperatures,chlorophyll index, relative water content, leaf water potential, proline content and yield were controlled by additive effects under mild stressed conditions. Under severe stress conditions however, canopy temperatures, leaf water potential and proline content were controlled by additive effects, while chlorophyll index and relative water content were controlled by both additive and dominant effects, as seed yield was mainly influenced by the dominant effects. The narrow sense heritability ranged from 47-97% for all traits, except for chlorophyll fluorescence. Yield correlated positively with chlorophyll index and relative water content, and negatively with canopy temperature and leaf water potential. Therefore, under drought stressed conditions in breeding programs, canopy temperatures, chlorophyll index and relative water content can be reliable criteria for the selection of tolerant genotypes with prospect to higher yields.
Highlights
Drought presents serious limitations to crop growth and productivity
We extended the number of influential traits as well as developing two distinct stress levels in order to investigate gene actions in affected lines
Different water levels were developed by irrigating the non-stressed plots at regular intervals (W1) while two levels of drought were developed by mild water stress, from the beginning of button stage (R4) (Schneiter and Miller, 1981) to start seed filling (R6), (W2) and applying a severe water stress which started from the beginning of button stage (R4) to physiological maturity (W3)
Summary
Drought presents serious limitations to crop growth and productivity. Water stress decreases plant growth and productivity by slowing the rate of cell division and expansion, mainly due to loss of turgor and afterwards the effect of reduction of the water status components of the plant cells (Tezara et al, 2002).Plant breeding approaches are looking for ways to hinder the effects of drought-driven problems. The selection of suitable genitors, with a good general combining ability, for example, is one of the most important steps in a hybridization program. Identification of the gene(s) responsible for the desired characteristics, like of drought resistance at different stages of plant growth and development, is of great importance (Dhanda et al, 2002). Breeding programs can take advantage of such information on combining ability to find better selection strategy for developing high yielding lines and hybrids (Skoric, 1992). Breeding programs and environmental conditions including drought stress can influence the evaluation of combining ability of sunflower genotypes (Petakov, 1996). To develop cultivars yielding better under drought stress, breeder needs information about the gene action of the traits related to yield and quality responsible for drought tolerance (Eshghi et al, 2010). Because direct selection based on agronomic traits in sunflower were shown to be complicated by low heritability of yield, indirect selection via yield components and other traits could be more efficient if these traits are related to yield and have a higher heritability than yield (Blum, Pourmohammad A. et al / Not Sci Biol, 2014, 6(2):207213
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