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Abstract
‘Sunburst’ is a moderately vigorous, precocious citrus hybrid with attractive, high-quality fruit (Fig. 1) of the tangerine class developed in the Florida breeding program of Agricultural Research, Science and Education Administration, of USDA.
Abstract
Seed of ‘Pineapple’ orange [Citrus sinensis (L.) Osbeck] and ‘Duncan’ and ‘Foster’ grapefruit (C. paradisi Macf.) were exposed to gamma rays at 10, 15, 20, 25, and 30 krad. Seedling emergence was delayed. LD50 levels were 10-15 krad for ‘Pineapple’, 15 krad for ‘Duncan’, and ≤10 krad for ‘Foster’. The greater sensitivity of ‘Foster’ may have been due in part to higher seed moisture content at treatment. Seedless mutants were obtained following gamma irradiation and fruiting of small numbers of seed and seedlings. The frequency of seedless mutants of ‘Pineapple’ and ‘Duncan’ was highest following treatments of 20-25 krad.
Abstract
Buds from a mature ‘Foster’ grapefruit (Citrus paradisi Macf.) tree were exposed to 3, 5, 7, 9, and 11 kilorad (kr) of gamma irradiation. The irradiated buds were grafted to rootstocks in the nursery and greenhouse. The LD50 was near 5 kr for buds grafted in the greenhouse and 9 kr for those in the nursery; however, no buds receiving more than 5 kr initiated growth. Grafted trees that grew were field grown until fruiting and seed per fruit was counted. Several nonjuvenile, commercially seedless clones were developed among small populations of plants, and in significantly less time than required through seed irradiation.
Abstract
Tree and fruit losses from cold injury are important problems in growing citrus. Severe losses from the freezes of 1894-95, 1957-58, 1962, and 1970-71 in Florida; 1949, 1950, and 1962 in Texas; and 1913, 1937, 1949, and 1950 in California, have stimulated research on cold hardiness of citrus. One method of reducing losses from freezes is the production of cold hardy cultivars by breeding and selection. Citrus physiologists and breeders with the USDA at Orlando, Florida; Indio, California; and Weslaco, Texas, have coordinated their research to develop more cold hardy citrus cultivars (2, 3). This paper summarizes some recent efforts to develop methods for screening citrus hybrids for cold hardiness. The glossary (Table 1) of the citrus types and names used here include cold hardiness ratings. Common names or a designated number will be used for simplicity of discussion.
Abstract
Nearly all commercial citrus trees are grafted, and the rootstock has a major effect on the performance of the scion cultivar. A citrus tree’s resistance to or tolerance of disease, nematodes, salt, cold, and other factors may be influenced by the rootstock. Also, the rootstock affects the tree’s adaptability to various environmental factors, as well as the quantity and quality of fruit that it produces. No available rootstock possesses all of the desirable traits needed by the citrus industry. Also, changes in culture and production problems create new demands.
Abstract
Effects of storage time, temperature, fruit preparation, time of harvest and number of diphenyl pads per carton with ‘Dancy’ (Citrus reticulata Blanco) and ‘Sunburst’ a seedling from ‘Robinson’ × ‘Osceola’, each C. reticulata × (C. paradisi Macf. × C. reticulata) tangerines were studied to determine the amount of diphenyl absorbed and extent of decay. Storage of ‘Dancy’ and ‘Sunburst’ at 4°C for up to 4 weeks with 1 or 2 diphenyl pads resulted in diphenyl residues less than the U.S. legal tolerance of 110 ppm. However, storage of both cultivars for 2 weeks at 21°C with 2 diphenyl pads resulted in residues exceeding this tolerance limit. Decay and diphenyl residues both tended to be higher for ‘Dancy’ than for ‘Sunburst’. ‘Dancy’ tangerines stored for 4 weeks at 21°C all decayed. Statistical examination of 2 harvests of ‘Sunburst’ showed that early harvested fruit were less susceptible to decay but prone to absorb higher amounts of diphenyl.
Abstract
In an assessment of natural hazards on world crop production, an average of more than $ 100 million per year is lost in the continental United States due to freeze damage to 22 major crops. The greatest loss is in citrus production and amounts to about one-third of the national average. A severe freeze occurred in 1962 which cost Florida more than one-third of its total production, in excess of 10 million boxes (41 kg.) of fruit and onefourth of its 52 million trees. Similar losses occurred again in 1977 and, most recently, in 1981 and 1982. These losses impact negatively not only on the present and future economic stability of an industry, but also in meeting the dietary needs (supply and nutrition) of an expanding world population, which is facing ever-increasing uncertainties in adequate nutrition and subsistence levels.