CROP PHYSIOLOGY & METABOLISM Physiological Consequences of Moisture Deficit Stress in Cotton

in determining how a plant responds to moisture deficit stress. Moisture deficits can depress cotton (Gossypium hirsutum L.) lint Although there has been considerable research docuyield in all cotton production regions. However, most cotton physiomenting the growth and physiological response of cotton logical drought stress research has been conducted in arid production to moisture deficit stress, most of it has been conducted regions, growth chambers, or greenhouses. The objective of this research was to document the effects of moisture deficit stress on the with pots in artificially controlled growth environments physiology of cotton grown in the humid southeastern USA. Field of greenhouses (Jordan, 1970; Radin, 1981; Radin and studies were conducted under dryland and irrigated conditions from Ackerson, 1981; Loffroy et al., 1983; Ball et al., 1994) 1998 to 2001 with eight genotypes, including an okra-normal leaftype and growth chambers (Genty et al., 1987; Nepomuceno near-isoline pair and transgenic lines paired with their recurrent paret al., 1998), or has been conducted under field condients. Dry matter partitioning, light interception, canopy temperature, tions in arid climates (Turner et al., 1986; Puech-Suanzes leaf water potential, gas exchange, chlorophyll (Chl) fluorescence, and et al., 1989; Ephrath et al., 1990; Ephrath et al., 1993; leaf Chl content data were collected. Genotypes responded similarly to Leidi et al., 1993; López et al., 1995; Lacape et al., 1998; both soil moisture regimes. Drought stress reduced overall plant statLeidi et al., 1999) where moisture deficit stresses are ure with a 35% leaf area index (LAI) reduction, prompting an 8% remore prevalent and extreme. Field studies under temperduction in solar radiation interception. Dryland leaves had 6% greater ate humid conditions have been conducted by McMiCO2 exchange rates (CER) and 9% higher light-adapted photosystem chael and Hesketh (1982) and Faver et al. (1996). From II (PSII) quantum efficiency than irrigated leaves during the morning. However, as water potential of the dryland plants became more dethese studies, we know that moisture deficit stress propressed during the afternoon, the CER and light adapted PSII quanmotes stunted growth in cotton with reduced leaf area tum efficiency of the dryland plants became inhibited and was 6 and expansion (Turner et al., 1986; Ball et al., 1994; Gerik 10% lower, respectively, than irrigated leaves. A 19% greater Chl conet al., 1996). Lint yield is generally reduced because tent for the dryland leaves contributed to their higher CER durof reduced boll production, primarily because of fewer ing the morning. This polarity of photosynthesis throughout the day flowers but also because of increased boll abortions for the dryland plants relative to irrigated plants may explain some of when the stress is extreme and when it occurs during the irrigation yield response inconsistencies in the southeastern USA. reproductive growth (Grimes and Yamada, 1982; McMichael and Hesketh, 1982; Turner et al., 1986; Gerik et al., 1996; Pettigrew, 2004). Leaf photosynthesis is also reA soil moisture (provided through timely and duced when plants are grown under moisture deficit conadequate irrigation or precipitation events) is esditions because of a combination of stomatal and nonsential for successful crop production. Upland cotton is stomatal limitations (McMichael and Hesketh, 1982; no exception to this requirement. Although wild cotton Marani et al., 1985; Turner et al., 1986; Genty et al., 1987; lines inhabit regions of sparse precipitation (Lee, 1984), Ephrath et al., 1990; Faver et al., 1996). As in most plants, irrigation technologies are necessary for the successful leaf water potential ( l) is reduced under drought condicommercial production of cotton in arid regions. Irrigations, but cotton has the ability to osmotically adjust tion scheduling in desert-like environments such as Ariand maintain a higher leaf turgor potential ( t) (Turner zona and California has been perfected to the point of et al., 1986; Nepomuceno et al., 1998). consistently producing acceptable yield enhancements Although these controlled growth environment studin cotton production (Radin et al., 1992). However, the ies have proven insightful, overall cotton growth and yield yield response of cotton to irrigation in the humid southis reduced when the root zone volume is constrained by eastern USA remains inconsistent (Pringle et al., 2003). a finite container size (Carmi and Shalhevet, 1983). How Understanding the nature of this inconsistent irrigation applicable these controlled-environment studies are to response requires a more thorough knowledge of cotton’s what the plants would experience and respond to under response to varying types of moisture deficit stress. The natural field conditions is not clear. Similarly, the arid timing, duration, severity, and speed of development for environment, where the vast majority of field studies the moisture deficit stress undoubtedly play pivotal roles have been conducted, would tend to lead to early, rapid, and extreme moisture deficit stress developing in the USDA-ARS, Crop Genetics and Production Research Unit, P.O. Box Abbreviations: CER, CO2 exchange rate; Chl, chlorophyll; DAP, days 345, Stoneville, MS 38776. Received 10 Nov. 2003. *Corresponding after planting; Fv/Fm, dark adapted chlorophyll fluorescence variable author ([email protected]). to maximal ratio; LAI, leaf area index; qP, photochemical quenching; PPFD, photosynthetic photon flux density; PSI, photosystem I; PSII, Published in Crop Sci. 44:1265–1272 (2004).  Crop Science Society of America photosystem II; qNP, nonphotochemical quenching; SLW, specific leaf weight. 677 S. Segoe Rd., Madison, WI 53711 USA