|Stipanovic, Robert - Bob|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2002
Publication Date: 3/1/2002
Technical Abstract: Cotton yields are affected by genetics, environment, and management. When cotton prices are low, producers tend to skimp on the latter. Environment can also alter pest pressure. For example, annual yields in Mississippi are inversely correlated with mean daily temperatures in July and August, the principal period of fruit set and boll maturation. One rationale would ascribe this correlation to heat stress, and the probable association of low rainfall with high temperatures. However, such trends are invariably confounded by the biology of the major pests that are infesting cotton during the same periods. For example, the life cycles of insect pests are accelerated by temperature, and high temperatures magnify moisture stress when root systems have been compromised by nematodes and diseases, as was frequently observed in 1999 and 2000. During the period of the 1990's major commercial cotton planting seed companies emphasized development of transgenic varieties with proprietary pest-managing traits. Based on their pest management efficacy, the transgenic varieties have increased their collective market share from no presence in 1994 to about 78% in 2001. However, these transgenic varieties were derived from transformed "Coker 312", an obsolete variety that is amenable to tissue culture. The transformed lines were then backcrossed with varieties that were top-yielding in the early 1990's, when such selections for backcross parents were the best available. Several generations were needed to produce agronomically acceptable transgenic varieties for commercial release. As a consequence of the time needed for variety development, the yields of the current transgenic varieties are comparable to those of the parent varieties that were originally developed about 10 years ago. Similar trends in the relation of yields of transgenic soybean varieties to those of currently developed non-transgenic soybean varieties have been observed. In general the results of breeding programs tend to reflect the breeding objectives. When emphasis is again placed on increasing yields, it is probable that yield potential of newly released varieties will again increase.