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- Author or Editor: James E. Pollard x
Application of 2-chloroethylphosphonic acid (ethephon) to ‘McIntosh apples’ in late August significantly increased development of anthocyanins in fruit peel, shortening the time to harvest by approximately 2 weeks. At higher rates of ethephon, treatment with succinic acid 2,2-dimethyl hydrazide (SADH) prior to ethephon applications was necessary to maintain fruit firmness. 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) contributed to excessive fruit cracking on the tree and in storage. SADH treatments were more effective than 2,4,5-T treatments in reducing accumulation of ethylene in stored fruit. Ethephon 50 ppm with SADH was more effective in producing desired fruit color, quality, and abscission characteristics than was the higher concentration of ethephon with SADH and 2,4,5-T.
A tissue macerating factor and pectinesterase activity were found in extracts from ‘McIntosh’ apple (Malus svlvestris, L.) during development of internal breakdown. Pectinesterase activity increased significantly and activity of the tissue macerating factor decreased significantly accompanying development of internal breakdown; concentrations of both remained low throughout development of the disorder. With loss of fruit firmness, fruit tissue water potential decreased as a result of decreasing solute potential and decreasing pressure potential. The first component of fruit firmness to decrease, tissue rigidity, is believed to decrease as a result of hydrolysis of intercellular pectins. The second component, cell turgor, decreased due to an increase in permeability of cell membranes to water in the later stages of development of internal breakdown. Decrease in both components of fruit firmness appear to contribute to tissue softening accompanying development of internal breakdown.
Two independent studies conducted in 1986-87 and 1987-88 provided evidence that rowcover-modified microclimate can enhance yield component development in strawberry (Fragaria × ananassa Duch. cv. Earliglow). Early autumn rowcover application in 1986-87 followed by removal at bloom increased mean diurnal temperatures and degree-day accumulation in autumn and spring compared with controls without rowcovers. For rowcovered plants, leaf growth continued longer in autumn and resumed earlier in spring, and more trusses and flowers were produced. In 1987-88, increased production of marketable fruit with rowcovers occurred in the absence of an increase in flowers and appeared to be primarily due to increased development of tertiary berries.
The tarnished plant bug (Lvgus lineolaris) is a serious pest of strawberries in North America, causing a severe malformation of the receptacle known as “apical seediness” or “buttoning”. Light and scanning electron microscopy were used to assess tarnished plant bug feeding on strawberries and to determine the nature of the injury. During early fruit development stages (anthesis to petal fall) the primary feeding sites were developing achenes. Feeding sites on more developed fruit changed to receptacle tissue, usually close to an achene. The “buttoning” malformation of strawberries associated with tarnished plant bug is most likely a result of the destruction of achenes during early fruit development stages. Feeding on receptacle tissue later in fruit development causes more localized damage, such as creases and indentations.
Greenhouse experiments were designed to study conditions affecting strawberry malformation caused by the tarnished plant bug (TPB). Duration of blossom exposure to TPB affected the type of malformation. Exposure at anthesis for 8 hours caused visible deformity. Exposure for 48 hours caused some apical seediness, the malformation most commonly associated with TPB. Continuous exposure to TPB usually caused blossom death. Increased exposure to TPB caused a higher percentage of nonviable achenes per strawberry. Some effects appeared to be cultivar-dependent. Honeoye strawberries were less likely to show apical seediness than Redchief strawberries, but were more likely to experience blossom death. Malformation was also affected by strawberry development stage at the time of TPB feeding. Feeding at prebloom caused blossom death. Feeding at petal fall or achene seperation resulted in fruit malformation, about half of which was apical seediness. Feeding at pink receptacle stage caused little visible damage.
Over-wintering strawberry (Fragaria × ananassa Duch.) plants under row-covers applied in early Fall 1983 through 1985, and removed in spring at first bloom, significantly increased production of marketable fruit. Spunbonded rowcovers of nylon or polyester were more effective than those of slitted polyethylene. In years when winter injury affected fruit production in noncovered controls, addition of a winter-protective mulch to rowcovered treatments in early December had no effect on fruit production, compared to rowcovered treatments without winter mulch. In years when winter injury was not a factor affecting production, addition of winter mulch to rowcovers nullified the rowcover effect on production. Accumulation of degree days (base 10°C) in soil and air in rowcovered plots was significantly greater than in noncovered plots. The rowcover effects influencing fruit production appeared to occur in winter and/or spring rather than in the fall.
Experiments were conducted to investigate the potential effect on floral bud initiation in strawberry (Fragaria × ananasa, cv. Chandler) by interrupting inductive short day cycles with a day-length extension treatment. Vegetative plants were exposed to 10-, 15-, or 20-day cycles of inductive short days in growth chambers. After receiving an inductive short day treatment plants were transferred to a greenhouse where they were exposed to non-inductive long days, which stimulated panicle elongation. Dissections of apical meristems immediately following each cycle of short days revealed that cycles of 20 days resulted in detectable floral bud formation. After 15 days in the greenhouse, all short day treatments had initiated floral buds. In the greenhouse, under long days, subsequent flowering in cohorts of plants which had previously received inductive short days showed a positive correlation between interruption of short days with day length extension and reduction in the number of floral buds initiated on earliest emerging panicles. These results suggest potential for manipulation of floral bud induction and potentially fruit size in Chandler, and perhaps other cultivars by interruption of a cycle of inductive short days with a day length extension treatment.
Rowcovers applied to strawberries have documented value for increased earliness and yield. The effect of rowcovers on insect damage to strawberries was investigated in this study. Nonwoven rowcovers were applied over strawberries in the fall with and without malathion to determine their effect on tarnished plant bug (Lygus lineolaris) and strawberry bud weevil (Anthomonus signatus) injury over two harvest seasons. Rowcovers increased the “umber and weight of marketable fruit. Tarnished plant bug injury was reduced by the use of rowcovers in 1990, regardless of insecticide application. I” 1991, rowcovers reduced tarnished plant bug injury only when a fall insecticide was applied. Rowcovers increased the number of flower buds killed by the strawberry bud weevil where no insecticide was used in 1990, but had no significant effect on the number of buds killed in 1991. The effect of rowcovers on insect injury to strawberries appears to depend upon the overwintering habits of the insects, and the prevailing weather patterns during a given season.