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The histology of external CO2 injury of the skin of `Empire' apples and postharvest factors affecting occurrence of injury were investigated. Injury was greater in a 5% CO2/2% O2 atmosphere than in 2% CO2/2% O2, but incidence was affected by orchard source. Susceptibility to injury was highest during the first 4 weeks of storage, while a postharvest treatment with diphenylamine prevented the disorder. Ethanol reduced injury, but ascorbic acid increased incidence of the disorder. Keeping fruit in air cold storage for 10 days before application of CO2 markedly reduced incidence of CO2 injury. Histological studies showed that external CO2 injury begins at the hypodermis—cortex boundary and spreads outward into the upper hypodermis and inward into outer cortex cells, although the cuticle and epidermis appear unaffected and unbroken. Radial walls of affected cells collapse and become pleated, so that the skin surface sinks below nearby normal regions. Other cellular events include loss of cytoplasmic integrity, coagulation of the protoplast, loss of organelle structure, and cell wall separation. Nondigested starch can be found in cells of affected fruit at the hypodermis—cortex boundary. We conclude that several factors affect fruit susceptibility to CO2 injury, including orchard, antioxidant treatment, and delays before application of CO2.

The objective of this study was to determine how nitrogen (N) supply affects the source-sink balance and fruit size of ‘Gala’ apple when crop load was controlled at a moderate level. Five-year-old ‘Gala’/‘M.26’ trees grown in sand culture and trained in tall spindle received a total of 3.3, 10.0, 20.0, or 40.0 g actual N through fertigation using Hoagland's solution from bloom to 3 weeks before harvest. The crop load of these trees was adjusted to 6.5 fruit/cm2 trunk cross-sectional area by hand thinning when the diameter of the largest fruit was 10 mm. As N supply increased, total shoot leaf area in the canopy increased, whereas total spur leaf area remained unchanged. Both single leaf and whole canopy net CO2 assimilation rates increased with increasing N supply. The net dry matter gain of the whole tree from budbreak to fruit harvest increased ≈74% from the lowest N supply to the highest N supply, but the proportion of net dry matter gain partitioned to fruit (harvest index) decreased from 83% to 70%. Both leaf area to fruit ratio and average final fruit size increased with increasing N supply, and a linear relationship was found between leaf area to fruit ratio and final fruit size. The number of cells per fruit increased with increasing N supply, whereas average cell size remained unchanged. As N supply increased, fruit soluble solids concentration increased, whereas fruit firmness decreased slightly. These results indicate that 1) apple trees grown under low N supply are source-limited; and 2) within the range of N supply used, increasing N supply improves leaf N status, leaf and whole tree photosynthetic capacity, and leaf area to fruit ratio, leading to more cells per fruit, larger fruit, and higher soluble solids.

Morphological and anatomical changes in shoots of vigorously growing cottonwood plants (Populus deltoides Bartr.) were studied during dormancy induction in 8‐hr short days (SD) and in control plants grown in 18‐hr long days (LD). Pronounced structural changes occurred in terminal buds after 4 wk and full dormancy was achieved in 7 wk of SD. Leaf expansion ceased after 5 wk of SD as foliage leaves matured to the terminal bud base at leaf plastochron index 0 (LPI 0). Within the bud, total leaf length (lamina + petiole) decreased and stipule length increased progressively each week; thus, the ratio total leaf length/stipule length decreased rapidly, especially at the position of incipient bud‐scale leaves LPI ‐ 1 and LPI ‐ 2. These bud‐scale leaves were fully developed by wk 6 and were derived from enlarged stipules and aborted laminae. The full complement of primordia within the bud at the start of SD eventually matured as foliage leaves and the first bud‐scale leaf (LPI ‐ 1) was initiated immediately following transfer to SD. Acropetal advance of the primary‐secondary vascular transition zone (TZ) was associated with leaf maturation. However, it did not advance throughout the entire vascular cylinder as in LD, but only in those leaf traces serving mature leaves beneath the terminal bud. In both LD and SD treatments the same linear relationship was maintained between LPI of the TZ and LPI of the most recently matured leaf; both parameters simultaneously increased in LD and decreased in SD. Thus, the relationship between leaf maturation and advance of the TZ was maintained irrespective of environment.

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Field and greenhouse studies were conducted from 1997 to 2001 to determine cabbage response to posttransplant applications of pendimethalin (0.56 to 2.24 kg ai/ha). Differential variety response was minimal, and applications greater than 0.56 kg caused severe and persistent crop injury and reduced head number and yield in ‘Azan’, ‘Storage 4’, ‘Super Elite’, and ‘Super Red 90’. Pendimethalin (1.7 kg) applied posttransplant reduced cabbage yield weights 23, 30, and 87% with bare root, large, and small transplants, respectively. Application (0.84 kg) to soil, foliage, or soil and foliage caused 0, 81, and 82% dry weight reduction by 21 d after treatment, respectively. Anatomical analysis of two-leaf seedlings collected 3 wk after pendimethalin treatment (1.12 kg ai/ha) showed stunting of the shoot apical meristem and its emerging leaves, disorganization of apical structure with disruption of normal cell division and cell expansion, and abnormal differentiation of the vasculature in leaves and hypocotyls.