An experiment was conducted in Phoenix in 1986 to determine effects of water and N deficits on ABA and IAA concentrations in young bolls and their abscission zones in relation to boll retention, and to determine the effects of N on growth of fruiting branches through the season. Water deficit decreased boll retention, decreased the concentration of free IAA in bolls and their abscission zones, and increased ABA in bolls and abscission zones. But, the concentration of ester IAA increased with water deficit (in contrast to free IAA). Because ester IAA resists degradation during stress, it may facilitate recovery when stress is relieved and some of it is converted to free IAA. N-deficiency symptoms were mild and did not appear early in the season. N had no effect on the ABA and IAA contents of bolls and their abscission zones, and had only a small effect on growth of fruiting branches. The N test is to be repeated in 1987 when N deficiency should be more severe.

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Plant growth products manufactured by BioHumaNetics, Inc. were evaluated in 1986 for a second consecutive year in the same field at the Maricopa Agricultural Center. Treatments included: 1) no fertilizers added, 2) standard fertilization recommended for the farm, and 3) a treatment schedule prescribed by BioHumaNetics. The non fertilized treatment had a significantly lower total yield than the two fertilized treatments.

PIX was applied to cotton in 10 and 20 gallons of water to evaluate the effect of dilution rate on plant growth regulation. No statistical differences were seen at the one pint rate, but the trends looked like the higher rate of water increased the plant growth regulation (i.e., decreased plant height and increased yield). Increasing the rate of PIX to 2 pints in 20 gallons of water, to maintain the same concentration as 1 pint in 10 gallons of water, was detrimental to the yields.

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The third year was completed of a study designed to evaluate the effects of Burst Yield Booster, a cytokinin based plant growth regulator, on upland cotton. Five treatments were included in the 1986 experiment, which varied application timing, rate, and frequency. Consistent with our studies of the past two seasons, no significant differences in yield were observed.

Afield study was conducted in Yuma County to evaluate the relative effects of a plant growth regulator application and several defoliation treatments on Pima cotton. There were no statistically significant effects recorded with regard to the plant growth regulator application. There was a significant difference among defoliation treatments by analysis of percent leaf drop estimates. Promising results were recorded for DROPP as a defoliant material for Pima cotton under the given test conditions.

Four short staple cotton varieties were grown with and without an application of PIX to see its affect on their growth, maturity and yield. PIX is a plant growth regulator thatmodifies plant architecture, Two of the tall -statured varieties, Delta Pine 90 and Acala 1517-75, showed increases in lint yield of 5.8 and 13.7%, respectively, coupled with a hastening of their maturity. Stoneville 506, a short- statured, medium- maturing variety was unaffected by the plant growth regulator. A tall, gangly variety, Germains GC 365, was shortened in height and in maturity, but exhibited a small decrease in yield.

Hormone analyses were conducted to determine why large squares seldom shed while young bolls do. Large squares contained five times as much free auxin as flowers, and they contained 16 times as much bound auxin. The high auxin content of large squares is probably a major reason that they almost never shed unless injured (for example, by insects). Free and bound auxin both decreased to very low levels at flowering and remained low for four days thereafter. This low concentration of auxin at, and just after, flowering is probably a major reason that bolls are likely to shed during the week after flowering. Both free and bound auxin increased rapidly between 7 and 9 days after flowering, possibly accounting for the decrease in boll shedding rate at this stage of development. Amide-linked IAA was the major form of auxin in squares, whereas ester IAA (presumably bound to sugars) was the major form of auxin in bolls.