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The concept that ethylene is an endogenous growth regulator has evolved in the past few years (16). This concept has been strengthened by recent findings that internal concentrations of endogenous ethylene in vegetative tissues reach physiologically active levels (3,12,13). These internal concentrations have been directly related to the corresponding production rates of excised tissues (13), although parallel data on production rates of intact plant tissues are not available. Using excised abscission zones from primary bean leaves, Jackson and Osborne (9) presented evidence that the timing of abscission of explant petioles can be related to the extent of ethylene production adjacent to the separation zone. They suggest that the ethylene production is coupled to a particular stage of senescence. Further, they proposed that in natural leaf abscission ethylene initiates the biochemical sequences leading to separation, but the mechanism is not clear. Beyer and Morgan (4) have recently shown that ethylene production by and internal levels in detached cotton cotyledons increases as auxin transport declines. Amounts of exogenous ethylene necessary to induce abscission and inhibit auxin transport were similar. They propose that the rise in ethylene production and decline in auxin transport capacity are causally related and that reduced auxin transport is one of the ethylene mediated actions which precede induction of hydrolytic enzymes in the separation layer. Their measurement of ethylene involved whole cotyledons and was not restricted to the petiole. McAfee and Morgan (13) found internal ethylene levels and production rates were several times higher in petioles than leaf blades. Since auxin must be translocated through the petiole to the abscission zone, this observation strengthens the proposed role of ethylene in auxin transport inhibition preceding cotton leaf abscission (4). Alternatively, high rates of ethylene production by petiole tissue near the abscission zone may directly trigger the biochemical changes preceding separation independent from the proposed effect on auxin supply to the abscission zone.Aside from abscission related to senescence, little attention has been directed to other problems of natural abscission, particularly those involving environmental stresses. Plant water deficits may induce both leaf and boll abscission from cotton under field conditions (5, 6, 18). In most instances, actual separation follows relief from the deficit and rehydration of the abscission zone. This communication describes the effect of a brief period of water deficit on ethylene production by intact cotton petioles. MATERIALS AND METHODSCotton plants (Gossypium hirsutum L. var TM-1) used in this study were grown in pots containing sand in a greenhouse and were between 75 and 90 days of age. Each pot contained two plants of equal size, each with 15 to 17 leaves on the main stem. The use of paired plants made possible the determination of leaf water potential on one plant, while ethylene production was measured on the ...

Premature boll shedding is characteristic of the cotton (Gossypium hirsutum L.) growth habit, but the extent of this shedding is quite variable. This study was undertaken to evaluate the effects of water stress on boll and leaf abscission. The experiments were conducted in a greenhouse using plants grown in pots containing sand. Plant water deficits were induced by withholding water. Leaf water potentials measured with a pressure bomb were used to quantify the plant water deficit. The extent of both boll and leaf abscission increased in a linear manner as leaf water potentials decreased from −10 to −24 bars. Abscission induced by water stress was dependent upon age of the tissue. Older leaves were shed as a result of relatively mild water deficits, while juvenile leaves did not abscise even after severe water deficits. Young, immature bolls were most sensitive to water stress. Bolls that remained on the plant approximately 14 days were retained by the plant even after exposure to a severe plant water deficit. A predawn leaf water potential of about −8 bars was required to induce significant leaf abscission.

Brown stink bug, Euschistus servus (Say) (Heteroptera: Pentatomidae), damage on developing corn, Zea mays L., ears was examined in 2005 and 2006 by using eight parameters related to its yield and kernel quality. Stink bug infestations were initiated when the corn plants were at tasseling (VT), mid-silking (R1), and blister (R2) stages by using zero, three, and six in 2005 or zero, one, two, and four bugs per ear in 2006, and maintained for 9 d. The percentage of discolored kernels was affected by stink bug number in both years, but not always affected by plant growth stage. The growth stage effect on the percentage of discolored kernels was significant in 2006, but not in 2005. The percentage of aborted kernels was affected by both stink bug number and plant growth stage in 2005 but not in 2006. Kernel weight was significantly reduced when three E. sercus adults were confined on a corn ear at stage VT or R1 for 9 d in 2005, whereas one or two adults per ear resulted in no kernel weight loss, but four E. servus adults did cause significant kernel weight loss at stage VT in 2006. Stink bug feeding injury at stage R2 did not affect kernel damage, ear weight or grain weight in either year. The infestation duration (9 or 18 d) was positively correlated to the percentage of discolored kernels but did not affect kernel or ear weight. Based on the regression equations between the kernel weight and stink bug number, the gain threshold or economic injury level should be 0.5 bugs per ear for 9 d at stage VT and less for stage R1. This information will be useful in developing management guidelines for stink bugs in field corn during ear formation and early grain filling stages.

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