Maturity and leaf shape as traits influencing cotton cultivar adaptation to dryland conditions

Worldwide, unreliable rainfall is the primary limitation to dryland cotton (Gossypium hirsutum L.) yields. Adaptation to these water stress environments has been and still is an important component of many crop improvement programs. This paper summarizes the results of cultivar experiments across three sites and six seasons comparing irrigated and dryland environments in Australia, with the objective of determining the extent of irrigation x cultivar interactions for yield and fiber quality, the effect maturity and leaf type have on those interactions, and the implications this has for a breeding program. On average, dryland cotton yielded 48% of irrigated cotton, and fiber lengths were 4% shorter. There was a significant irrigation x cultivar interaction, with two okra leaf cultivars yielding relatively more under dryland conditions. This interaction varied with site, suggesting that the number of dryland sites utilized in the breeding program could be increased, and consistency of cultivar rankings each season indicated the number of testing seasons could be decreased. It was also concluded that selection under dryland conditions would be beneficial. The data from these experiments indicated a yield penalty for early maturing cultivars under dryland conditions in these environments. There was a strong positive association between maturity and lint yield, with an increase of 34.4 kg lint ha(-1) for every day delay in maturity. Agronomic water use efficiency (WUE) varied among cultivars, with a full-season okra leaf cultivar, Siokra L23, having the highest WUE (2.87 kg lint ha(-1) mm(-1) evapotranspiration) and the highest yield.