In two cultivars of bean (Phaseolus vulgaris L., Redkloud and Redkote) the older fruits growing at the base of racemes aborted less frequently than the younger ones above them. When older fruits at the base of racemes were removed, the abortion rate of the younger ones was reduced and their abscisic acid (ABA) concentration was lowered. Thirteen days after fruit removal, 36 to 45% of the younger fruits remained viable on treated plants while less than 12% of the younger fruits were viable on control plants. On these intact controls the ABA concentration of young fruits was at least twice that of defruited plants. A similar difference was found when the ABA content was expressed on a per fruit basis, suggesting a direct regulatory influence of older fruits over the ABA content of younger fruits.Premature fruit abscission, often of a large percentage of fruits on a plant, is a common phenomenon that has been reported for a number of plant species including apples (9), beans (15), and cotton (4,8). In beans, abscission appears to be the last step in the process of fruit abortion, which is characterized by cessation of seed development, flattening of pod walls, and loss of green color (15). Events leading to fruit abortion may include a decrease in the concentration of auxins (9) and an increase in the concentration of ethylene and ABA (4,8). However, neither the regulation of these hormonal changes within a fruit nor the coordination of fruit abortion with over-all plant development is well understood.In the companion article, fruits were shown to inhibit the growth of axillary buds of bean plants (15). The present report describes the competitive inhibition of young fruits by adjacent older fruits of bean plants. MATERIALS AND METHODSBean plants (Phaseolus vulgaris L. cv. Redkloud and cv. Redkote) were grown in a controlled environment growth chamber. The conditions of plant growth and methods of ABA analysis were described in the companion paper (15). The effect of older fruits on the abortion rate and ABA content of the younger ones was tested as follows. Fruits within each raceme were classified into categories of "older" (those at the base of the raceme), "younger" (those in the upper part of the raceme), and "aborting" RESULTS Effect of Older Fruits on the Growth and Abortion of YoungerFruits. The relative age of developing bean fruits within a raceme affected their rate of abortion: older fruits at the base of the raceme aborted less frequently than the younger ones above them. When the older fruits were removed from each raceme, the abortion rate of the younger fruits greatly decreased in both cultivars (Table I). On treated plants (older fruits removed), 36 to 45% of the younger fruits remained viable, while on controls the number was below 12%. Only 18 to 33% of the older fruits aborted on control plants. The effect of older fruit removal was highly significant, as shown by analysis of variance, on the number of viable younger fruits (F = 45.5, P = 0.001). Over 82% of the total variation in young...

A comparison was made of the germination, growth, and leaf CO2‐exchange rates of redroot pigweed (Amranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) under varied temperature regimes. It was found that redroot pigweed had greater rates of germination, growth, and CO2‐exchange rates at high temperatures, whereas common lambsquarters performed better at low temperatures. The implications of such characteristics for competition between these species of weeds and their effect on crops are discussed.

Two dry bean (Phaseolus vulgaris L.) cultivars were grown in controlled‐environment chambers under standard light [390 μ Einsteins m‐2 sec‐1 (400 to 700 nm) = approx. 22,000 lux] and shaded light [55 μ Einsteins m‐2 sec‐1 (400 to 700 nm) = approx. 3,200 lux] intensities. Experimental observations included measurement of gas exchange and photosynthetic and respiratory enzyme activity along with examination of plant morphology, leaf anatomy, and chloroplast ultrastructure.Shading reduced leaf number, area, and thickness. Photosynthesis/unit area of shaded leaves was decreased by an average of 38%. Transpiration was not significantly affected. Increased intracellular resistance of the shaded leaves was more important in reducing CO2 uptake than was the increase in stomatal resistance. The increase in mesophyll resistance was reflected both in the biochemical reactions of the leaf (activity of all measured enzymes being reduced by 70%) and in the ultrastructure of the leaf chloroplasts (reduced quantities of starch in spite of extensive grana).

Chilling of mature-green (MG) tomato fruit (Lycopersicon esculentum Mill. and related species) was investigated to determine the effect of chilling stress on surface color during low-temperature storage. Color measurements were made with a tristimulus calorimeter (L, a, b values), and data were analyzed by multivariate analysis of variance and canonical variates analysis. Changes in surface color of MG fruit during chilling were not correlated overall with relative chilling sensitivity of cultivars/lines; however, within standard and cherry types, chilling-tolerant fruit changed surface color more during chilling than chilling-sensitive fruit when fruit were picked early in the season. Early harvests were less chilling-sensitive than late harvests. The number of hours below 15.6C in the 200 hours before harvest was positively correlated with postharvest chilling sensitivity. A high vs. ambient relative humidity during storage did not affect chilling-induced percent change in color. Tobacco mosaic virus resistance led to less and Verticillium albo-strum Reinke & Berthier resistance led to more chilling-induced color change. There was no effect from resistances to Fusarium oxysporum Schlechtend f. sp. lycopersici (Sacc.) W.C. Snyder & H.N. Hans, alternaria stem canker (Alternaria solani Sorauer), anthracnose [Colletotrichun coccodes (Wallr.) S.J. Hughes], root-knot nematode (Meloidogyne hapla Chitwood), Phytophthora infestans (Mont.) deBary, or Stemphylium botryosum f. sp. lycopersici Rotem, Cohen, & Wahl. Our results show harvest date had an effect on chilling-induced changes in surface-color in MG fruit.