Genetic Variation for Gas Exchange Rates in Grain Sorghum

Abstract

Carbon assimilation rate (A) and stomatal conductance (g) are highly correlated. However, the slope of the A versus g relationship differs among species and environments resulting in differences in gas exchange efficiency which should reflect water use efficiency. The objective of this research was to determine the genetic variation for A and g in grain sorghum (Sorghum bicolor [L.] Moench.). Field experiments were conducted using 30 sorghum hybrids with four water supply treatments. A, g, and leaf water potential ( ¶',) of individual leaves were monitored every 15 to 20 days. Significant genetic variation existed among the hybrids for A and g. Plant age and water supply also affected A and g as expected. When A was regressed on g for each hybrid, large and significant differences existed among the slopes, implying differences in intrinsic gas exchange efficiency. The regression analysis of A and g versus ',, suggested that A was more sensitive than g to increasing water stress. Genetic differences in the rate of change in A as water stress increased were observed. Regression analysis was used to evaluate the individual hybrid response relative to other hybrids. Twofold difference in slopes existed for A. These results provide evidence for genetic variation in gas exchange rates which might directly contribute to whole plant water use efficiency and productivity.

Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines

“…These results agree with the report of Kidambi et al (1990) who evaluated 30 grain sorghum hybrids grown under field conditions using four different water supply treatments. They reported significant genotypic variation in leaf photosynthesis both across the season and in any given sampling time-irrigation level combination.…”

Parental influences on gas exchange rates in grain sorghum

“…Only limited information exists concerning the genetic variation in A or g to increasing water stress (Henzell et al . 1976 ;Kidambi et al . 1990) .…”

“…Since the maternal effects were important in causing these reciprocal differences, it may be possible to utilize the vigor by selecting specific female parents to improve A in sorghum . Since A exhibited a strong genetic control and g responded more to environment, and due to the substantial genetic variation among the hybrids for slopes in A-g relationship (Kidambi et al ., 1990), opportunity exists to impose selection on improved A in the sorghum hybrids for increased WUE .…”

“…Recent evidence for wheat (Triticum aestivum L.), peanuts (Arachis hypogea L.), and sorghum [Sorghum bicolor (L.) Moench] indicates that carbonisotope discrimination can be used to investigate variation among genotypes for both productivity and WUE (Condon et al ., 1987 ;Farquhar & Richards, 1984 ;Hubick et al ., 1986Hubick et al ., , 1990 . We have demonstrated that significant genetic variation exists for both A and g in grain sorghum hybrids (Kidambi et al ., 1990) . Although A and g are coupled, the rate of change in each is not constant as the environment changes, resulting in variation in the A : g ratio .…”

Genetic analysis and phenotypic characterization of leaf photosynthetic capacity in a sorghum (Sorghum spp.) diversity panel

“…In sorghum, a strong correlation between A and stomatal conductance (g s ) was identified on a set of 30 sorghum lines under different water regimes (Kidambi et al 1990). Significant genetic variation in A and related physiological parameters was also identified in 22 (Peng et al 1991), eight (Henderson et al 1998), and five sorghum lines (Peng and Krieg 1992).…”