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Variation in soil water extraction and harvest index among peanut cultivars in response to drought

G.C. Wright

Queensland Dept. Primary Industries, P.O. Box 23, Kingaroy, Q. 4610

Studies on the adaptation of peanut to both intermittent and protracted drought stress are being conducted at Kingaroy to define suitable characters for selection of drought tolerant types in the breeding programme. Pod yield is analysed in terms of total water transpired through soil water extraction (T), efficiency of conversion of transpired water into dry matter production (W), and the proportion of dry matter partitioned to pods, or harvest index (HI). This paper reports variation in T and HI among peanut cultivars grown under a terminal drought stress treatment.


Two Virginia cultivars of 140 day maturity (Virginia Bunch (VB) and Q18801) and two Spanish cultivars of 120 day maturity (McCubbin and Red Spanish) were grown under rainout shelters from early pod set (50 days after planting) until maturity. The depth of soil water extraction and seasonal water use were measured by neutron probe, and total dry matter and its distribution to plant parts were recorded at maturity.

Results and discussion

Rainfall during the first 50 days amounted to 287 mm and ensured all plots had a full profile prior to treatment imposition. Severe crop water deficits developed late in the season and caused accelerated maturity in the Virginia types, with all cultivars having similar final maturity of about 120 days.

There were significant cultivar differences in seasonal water use (Table 1) which arose from differences in end of season soil water extraction. VB extracted about 40 mm more soil water than the other cultivars, with the extra water being extracted at depths between 0.8 and 1.6 m.

Table 1.Seasonal water use, total dry matter, pod yield and harvest index of peanut cultivars.

Pod yields differed between cultivars, with VB yielding significantly less than the other cultivars (Table 1). Pod yield was a function of the rate of pod addition and subsequent filling in response to plant water deficits. Pod numbers were high in McCubbin and Red Spanish because of earlier flowering and more synchronous pod set, and in Q18801 because of higher pod addition rates under stress. In contrast reproductive development in VB slowed dramatically in response to plant water deficits, and resulted in significantly reduced H1 (Table 1).

These results demonstrate substantial cultivar variation in T and HI. These characters were however not positively associated in the cultivars tested, for example, VB had good soil water extraction ability with poor HI. Further studies on associations between these characters across a larger range of cultivars is in progress.

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