The stramenopile plant pathogen Phytophthora capsici Leon. causes root, crown, and fruit rot on a large number of high-value vegetable crops ( Granke et al., 2012 ; Hausbeck and Lamour, 2004 ). Initially described by Leonian as a pathogen of
, and have frequently produced nonrepeatable results ( Huang et al., 1990 ; Williams et al., 1966 , 1967 ). Detached leaf assays have been used to maintain cultures of the crown rust fungus ( P. coronata ) from oats ( Avena sativa L.); however, it
Dormant rhubarb crowns do not force well until their rest period or physiodormancy (7) has been broken by sufficient chilling in the field during late fall. There are many reports that during exposure of dormant plants to cold, the free amino acids contents change. Asen and Stuart (1) found that dormant leaves and buds of Hydrangea macrophylla showed an increase of some free amino acids after 6 weeks of storage at 4 to 5°C. Another worker (8) reported that in one alfalfa variety there was a 20% increase of acids from August to December. Schneider (4) found that the levels of some free amino acids in leaves of Ilex crenata nigra rooted cuttings changed during storage at cool temperatures. In this study buds and roots of dormant rhubarb crowns were analyzed to determine the free amino acids present and also possible changes in acids levels that might indicate the end of the rest period.
Anthracnose crown rot and fruit rot caused by species of the fungal genus Colletotrichum produce significant losses in strawberry ( Fragaria × ananassa ) production with crown rot, resulting in plant death and fruit rot, which in turn results
Seed of asparagus (Asparagus officinalis L.) germinated normally after 2 months of constant freezing (-10°C) or chilling (4°) under water-saturated conditions in laboratory germination studies. However, temperatures cycling weekly from chilling to freezing for 2 months reduced germination to less than 50%, and temperatures cycling weekly from warm (21°/16°, day/night) to chilling to freezing for 2 months reduced germination to 0. The stands of asparagus, field-seeded in November and December, were reduced 85% by winterkill in comparison to spring seeding in March and April. Seeding densities from 10 to 40 seed/m did not compensate for stand loss. The greatest contributor to winterkill apparently was seed rot. March seeding increased plant height, but not crown quality or the number of shoots initiated in comparison to conventional April seeding. High seeding densities did not reduce plant growth or crown yields in the spring plantings. Stand establishment was not different between the spring planting dates. Early March seeding at high densities is recommended.
Ethylene (C2H4) was higher in the internal atmosphere of crown gall infected rose bushes than in healthy plants. C2H4 was higher in the crown and root tissues than in the top of normal as well as crown gall infected plants.
Growth studies of field-seeded hybrid and open-pollinated asparagus (Asparagus officinalis L.) were conducted to determine the differences in shoot, bud, and crown growth during the first season after seeding and to determine growth relationships between shoot and crown variables that indicate critical periods of bud and crown production. F1 hybrid (UC 157) and UC800 open-pollinated (OP) asparagus seedlings emerged 4 to 6 weeks after seeding. A lag phase of shoot and root growth lasted 4 to 5 weeks after emergence in both cultivars. UC157 initiated more roots and accumulated more fern and crown fresh weight than UC800 early in the season, but by harvest crowns were not different in root and bud number, fresh weight, or fructose content (crown quality). Root/shoot ratios increased from a 2:1 ratio 6 weeks after emergence to 8:1 (UC157) and 6:1 (UC800) 23 weeks after emergence. Shoot/bud ratios stabilized from an approximate 2:1 ratio initially to an approximate 1:2 ratio 18 weeks after emergence. Bud production in the F1 and OP cultivars increased 6 and 10 weeks after emergence, respectively, and continued unabated up to crown harvest 23 weeks after emergence. Shoot number and fresh weight were not correlated highly with bud number. The number of roots vs. buds and the crown vs. fern fresh weights were correlated highly and were the best indicators of quality crown production. Vigorous fern development throughout the growing season increased the potential to produce higher-quality large crowns.
-layer branch from the top to the bottom of the crown), the middle terminal bud (the terminal bud of the middle-layer branch of the crown), and lower terminal bud (the terminal bud of the bottom-layer branch of the crown). Samples were taken from four directions
Thermotolerance of pineapple crowns (`Champaka 153') to 50C and above was increased with a 30-min first treatment at 30, 35, or 40C. Pineapple crowns receiving a 30-min heat treatment, before a second heat treatment at 50 or 55C, exhibited significantly less leaf damage than controls receiving no first treatments (P ≤ 0.05). The degree of thermotolerance was dependent upon the season in which crowns were harvested; greater thermotolerance occurred in crowns harvested in April than those harvested in October. Maximum thermotolerance occurred after an interval of at least 8 h between the first treatment and the higher temperature heat treatment. Thermotolerance was stable for at least 24 h.
Crown gall incited by Agrobacterium tumifaciens is an important problem for nursery and field production of stone fruit and nut crops. Genotypes reportedly differ for crown gall reaction, but there is little information about resistance of Prunus accessions used as rootstocks. From among four wild-type strains of A. tumifaciens-virulent on apricot and almond, K12 was selected for inoculation of 6-month-old seedlings of cherry, plum, peach, almond, apricot, and miscellaneous species. The large majority of seedlings were very susceptible to crown gall, but some had few or no galls. Cherry, especially some lines of P. mahaleb, showed the most resistant or moderately resistant seedlings, while some accessions of plum, especially P. cerasifera, P. angustifolia, and P. insititia had the most resistant seedlings. Plants with different reactions were propagated to determine adult plant resistance and to study the heritability of crown gall reaction.