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Abstract
The subject of water relations in microbial growth and development of plant disease has been reviewed extensively (11, 13, 14, 18, 19, 28, 34), as has the subject of water relations of wood decay and growth of wood-decay fungi (20). This paper will not duplicate earlier reviews, except as necessary to present some basic principles. Our paper has 5 parts: 1) the water potential concept; 2) methods to measure water potential; 3) water potential requirements for growth of bacteria and fungi; 4) water potentials of the tissues of some fruits and vegetables after harvest; and 5) water potential and the development of disease.
Parthenocarpic pickling cucumbers may be advantageous to conventional nonparthenocarpic cultivars due to their higher fruiting capacity and ability to produce fruit under poor pollination conditions. The processing quality, particularly firmness, of parthenocarpic pickling cucumbers has been questionable. Fruit firmness of six parthenocarpic and six nonparthenocarpic cultivars was evaluated in 1992 at Brooks, Oregon. Plots covered with floating row covers, to prevent pollination and ensure parthenocarpic fruit set, were compared with noncovered plots. Parthenocarpic cultivars were significantly softer than nonparthenocarpic cultivars. Cultivars within the parthenocarpic and nonparthenocarpic types were significantly different from one another. Fruit produced under row covers were significantly firmer than those which were pollinated. Cultivars which were firmer under the row cover tended to be firmer in the absence of row cover. Floating row covers allow firmness and parthenocarpic fruiting ability to be evaluated concurrently.
The firmness of parthenocarpic (P) pickling cucumber cultivars is generally considered unacceptable for processing by the US pickling cucumber industry. Genetic improvement in firmness of P pickling cucumbers may increase their acceptability. Inheritance of fruit firmness (FF) in nonparthenocarpic (NP) cucumbers has been reported as quantitative but highly heritable with additive gene effects accounting for most of the genetic variation and no maternal effects. Genetic investigations were conducted at Brooks, Oregon, in 1992 and 1993 to determine the inheritance of FF in P cucumbers. High heritability for FF was found with most genetic variance attributed to additive gene effects when F1's from four P gynoecious inbreds as females and five NP monecious inbreds as males were used in 1992. Experiments in 1993, with inbred derived populations, revealed that dominant variance and maternal effects for FF may be substantial in certain populations with parthenocarpic germplasm.