No abstract

The three commonly used root-knot resistant peach rootstock Nemaguard, Nemared, and Okinawa are deficient in one or more desirable characters for areas with mild winters and sandy soils, such as are found in Florida. These rootstock are susceptible to Meloidogyne incognita (Kofoid and White) Chitwood race 3 root-knot nematode. Nemaguard and Nemared require more winter chill for proper fruiting than occurs in Florida. Okinawa has a low-chill requirement but produces an undesirable high percentage of double-seeded pits. Nemared has red leaves, an aid in debudding of green-leaved cultivars. Flordaguard has improved root-knot nematode resistance and single-seeded pits, and is low-chilling and red-leaved. It is released by the Univ. of Florida Agricultural Experiment Station for grower trial and is expected to become a standard peach rootstock for low-chill peach production in rootknot nematode infested nonalkaline soils.

No abstract

Breeding to adapt temperate-zone fruit to subtropical production areas has been a formidable objective because so many different characteristics have to be changed, most of which are controlled by many genes. Recurrent selection is the only breeding method that can accomplish the required wholesale reorganization of the physiology of the plant. The principles of recurrent selection, developed and tested using short-generation organisms like fruit flies, rats, and maize, have been applied to the development of low-chill highbush blueberry (V. corymbosum L.) and peach [Prunus persica (L.) Batsch.] cultivars for northern and central Florida. These principles include using many parents per generation of crosses, minimizing the time between cycles of selection, and selecting simultaneously for all heritable traits that are important in the final product, with traits of highest economic importance and highest heritability being given the highest weight in selecting parents. Many characteristics changed during the breeding of low-latitude peach and highbush blueberry cultivars, including chill requirement, photoperiod response, resistance to various disease and insect pests, fruit chemistry, and growth patterns during a long growing season.

Over several years, we obtained no hybrids after pollinating thousands of flowers of cultivated tetraploid highbush blueberry (Vaccinium corymbosum L. hybrids, section Cyanococcus) with pollen from diploid V. arboreum Marshall (section Batodendron, sparkleberry), a drought-tolerant blueberry relative native in the southeastern United States. In an effort to produce tetraploid V. arboreum that could be crossed with highbush blueberry, more than 30,000 seeds were soaked in aqueous colchicine (0.1% to 0.2%) for 24 h or more. The seeds were germinated, and putative tetraploid plants (selected based on morphological characteristics) were grown long enough to obtain pollen for microscopic examination. Twelve selected seedlings that produced unusually large pollen tetrads were used as pollen parents in crosses with more than 40 different tetraploid highbush cultivars and advanced selections. Eighty-six crosses, in which a total of 17,968 flowers were pollinated, gave 1,569 plants that were verified as hybrids after one growing season in the field. Hybrids varied from very weak to quite vigorous, some equaling highbush cultivars in vigor. A few vigorous hybrids were male-sterile, but most had at least some pollen fertility. Of the most vigorous F1 hybrids, 12 of the most fertile, based on the amount of pollen shed and on the microscopic appearance of the pollen, were backcrossed to highbush cultivars, and 3919 backcross seedlings were obtained. These varied widely in vigor but averaged higher in vigor than their F1 interspecific hybrid parents.