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Elimination of in vitro contamination and shoot multiplication were studied with Aglaonema Schott ‘White Tip’. Apparently, contamination was reduced, but explants browned when 200 mg·L−1 streptomycin was used as either a pretreatment or incorporated into the medium. Reduced occurrence of contamination and browning was achieved in axillary bud explants excised from the stock plants that had not been watered for 2 months. Six shoots per explant elongated normally in Murashige and Skoog (MS) medium containing 30 μm benzylaminopurine (BA). MS medium containing 20 μm thidiazuron (TDZ) also resulted in six shoots per explant, but these shoots failed to extend beyond a rosette. Only microcuttings from 30 μm BA treatment were used for the ex vitro rooting trial, and indole-3-butytric acid (IBA) at 9.8 or 19.7 mm applied to the base of the microcuttings resulted in 100% ex vitro rooting and the longest roots.
Abstract
When sprayed after anther dehiscence, captan (N-(trichloromethylthio) cyclohex-4-ene-1,2-dicarboxyimide) decreased strawberry achene set and berry development in the greenhouse and increased the proportion of misshapen fruits. Pollination of unsprayed pistils from sprayed anthers was not as effective in setting achenes as was control pollination of sprayed pistils. Sprays applied to pistils either just before or just after pollination decreased achene set. Achene set was not affected by spraying one day after pollination. Captan seemed to act directly upon pollen germination and neither upon the receptivity of the stigma nor upon pollen tube growth in the style or on fertilization.
Abstract
Captan has been shown to inhibit pollen germination of the strawberry when included in or sprayed on agar germination media, or when sprayed on anthers after dehiscence. Toxic effects did not disappear during prolonged germination. Pollen germination was slightly affected by captan sprayed on the undehisced anthers.
In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.
Postbloom fruit drop (PFD) of citrus is incited by the fungus Colletotrichum acutatum J. H. Simmonds and may result in young fruit drop and severe yield losses. Previous studies suggested that imbalance of growth regulators such as auxin, ethylene, and jasmonic acid (JA) plays an essential role in young fruit abscission. In this work, we determined the factors associated with fungal-induced fruit drop by testing compounds inhibitory to hormonal transport or biosynthesis. As assessed on sweet orange (Citrus sinensis Osbeck) and grapefruit (C. paradisi Macf.) for 4 years, we found that many auxin transport and action inhibitors such as 2,3,5-triiodobenzolic acid (TIBA), 2-(4-chlorophenoxy)-2-methyl-propionic acid (clofibrate), or quercetin and JA biosynthesis inhibitors such as salicylic acid (SA) and aspirin (methyl-SA) applied 7 d after C. acutatum infection resulted in higher percentages of young fruit retention compared with the water controls. The commercial products ReZist and Actigard, widely used as systemic acquired resistance (SAR) agents, also improved fruit retention. Furthermore, application of gibberellic acid (GA3) on sweet orange, regardless of C. acutatum infection, significantly increased fruit retention. These commercial products may be very useful in managing this destructive disease of citrus in the field.