fore tasseling) can result in shorter plants and smaller leaf area (Denmead and Shaw, 1960; NeSmith and Rit-Seed companies have commercialized new transgenic maize (Zea chie, 1992; Abrecht and Carberry, 1993), decreased wamays L.) hybrids that are resistant to European corn borer [Ostrinia nubilalis (Hü bner)]. Drought stress may affect the expression of Bt ter use due to the reduction in plant size (Robins and proteins in maize tissues, and its resistance to European corn borerThe study was conducted at the Hinds Irrigation Farm, Iowa State University, Ames, IA, during the summers of 1997The effect of water deficit on maize growth and develand 1998. The experimental plots were 1 m deep, 123-L plastic opment has been studied extensively. The results indicontainers filled with soil and buried with the rim at ground cate that water deficit during the vegetative period (belevel. The soil in the containers was collected from the 0.15-m upper layer of a Nicollet loam (Aquic Hapludolls).
Forage quality of alfalfa (Medicago sativa L.) often is higher in water‐deficit‐stressed plants than in nonstressed plants. At least part of the improvement could result from a delay in plant development due to the water stress. The objective of this study was to determine forage quality response of alfalfa to water stress and to relate this to corresponding changes in plant maturity, phonological development, and growth. ‘Apollo II’ alfalfa was grown in 100‐L containers set into the ground and protected by a movable rain shelter. Plants were watered either weekly or twice weekly to 112,100, 88, 76, and 64% of field capacity during 2 yr. Regrowth herbage was harvested at five weekly intervals beginning 3 wk after the initial cut. Plants were divided into stem bases (portion of stems below and including the sixth node), stem tops, and leaves before forage quality analyses were conducted. Plant maturity decreased linearly with increasing water stress. Averaged over the harvests, leaf‐to‐stem ratio (LSR) increased from 0.60 in the well‐watered treatments to 0.72 in the most severely stressed treatment. Delayed plant maturity and node number did not account fully for the increase in LSR under water stress. In vitro digestible dry matter (IVDDM) in stems, which increased by about 9% under water stress, was largely accounted for by delayed plant maturity. In stem bases, crude protein (CP) concentration increased by 11% with increasing water stress, even after accounting for differences in plant maturity. Cellulose concentration, expressed on a cell‐wall (CW) basis, decreased whereas CW hemicellulose concentration increased with water stress in both leaves and stems, and these changes were not entirely attributable to differences in plant maturity and growth. Thus, the slowing of plant maturation and growth during water stress accounted for much, but not all, of the changes in forage quality.
Limited soil moisture influences field crop performance by reducing plant height, the size of the assimilating leaf area, and the size and number of potential storage sites for produced dry matter. The effect of moisture stress on plants is complex and very dependent on the stage of development. Therefore, soybeans (Glycine max (L.) Merr.) cultivars ‘Hark’ and ‘Rampage’ were in grown in the field in large potometers filled with the top 15 cm of a Nicollet loam (Aquic Hapludolls, fineloamy mixed mesic). The plants were subjected to four independent moisture stress periods during critical reproductive stages of growth. Soil moisture was controlled by hand watering and the use of an automatic weather shelter, which covered the plots during periods of rainfall. Soil moisture was measured with a neutron soil‐moisture probe, and frequent leaf‐water potential and leaf diffusive resistance measurements were collected to document moisture stress. Final seed yield and components of yield were determined at maturity for all experimental units. Moisture stress significantly affected most components for both cultivars during the four stress periods, but important cultivar moisture stress interactions were difficult to identify. Although these two cultivars differed greatly in some specific components of yield (Le., seed number, seed size, etc.), compensation between the different yield components resulted in no consistent yield differences between these two cultivars.
Drought stress can lower seed quality of soybean [Glycine max (L.) Merr.], possibly from stress related changes in seed‐nutrient concentration. Determinate soybean plants were grown under a mobile weather‐shelter near Ames, IA in 1985 and 1986 to determine if the timing of drought stress could influence seed‐Ca concentration and, subsequently, seed germination and quality. A randomized complete‐ block design was used to test the effect of withholding water during flowering (R2), full pod (R4), seed formation (R5), and full seed (R6) on the quality of the harvested seed. Drought stress was quantified by monitoring leaf temperatures. Each drought‐stress period received an equivalent amount of drought stress. Seed from a R5 drought stress had 85% germination compared with 96% germination for the nonstressed seed. This reduction in seed germination coincided with a 343 μg g−1 decrease in seed‐Ca concentration from a Ca level of 1648 μg g−1 in the nonstressed seed. Electrolytic conductivity per seed and seed‐Ca concentration were negatively correlated (r = −0.50). Germination percentage was significantly correlated (r = + 0.57) with seed‐Ca concentration and negatively correlated with P, Fe, and Zn (r = −0.49, −0.44, and −0.43, respectively). Application of 2.0 g L−1 of Ca(NO3)2 to the germination media of the R5‐stressed seed improved germination to the level obtained by nonstressed seed. The application of Ca(NO3)2 also improved the germination of R6‐stressed seed, which had a concentration of seed Ca equal to the control. This suggests that seed‐Ca concentration is not solely responsible for the decrease in germination percentage of drought‐stressed seed. Results indicate that drought stress during seed formation can reduce seed‐Ca concentration, but additional work is needed to clarify the role that Ca and other seed nutrients play in the germination of drought‐stressed seed.
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