One approach for obtaining useful genetic variation is to select for somaclonal variants generated by tissue culture techniques. Increased levels of resistance to bacterial leaf spot (Xanthomonas campestris pv. pruni) have been observed in toxin-selected and unselected peach regenerants in vitro, in the greenhouse and under field conditions. Peach regenerants have also demonstrated increased levels of bacterial canker (Pseudomonas syringae pv. syringae) and root-knot nematode (Meloidogyne incognita) resistance. Random amplified polymorphic DNA (RAPD) primers have been used to study genetic variation at the DNA level among the somaclonal variants. Sixty RAPD primers (10-mers) were screened and 10 proved useful as markers to detect polymorphisms, thus establishing a genetic basis for somaclonal variation. These studies demonstrate the feasibility of using tissue culture techniques to generate fruit trees with increased levels of disease resistance.
Freddi A. Hammerschlag, Ghazala Hashmi, Robin Huettel, Dennis Werner, and David Ritchie
Sergio J. Carballo, Sylvia M. Blankenship, Douglas C. Sanders, David F. Ritchie, and Michael D. Boyette
Commercial packing lines in Sampson County, N.C., were surveyed during two growing seasons to study handling methods on susceptibility of bell pepper fruits (Capsicum annuum L.) to bacterial soft rot (Erwinia carotovora subsp. carotovora). Samples were taken from two field packers and one packing house in 1991 and from two field packers and four packing houses in 1992. One field packer and one packing house were common to both years. Fruits were either inoculated with bacteria or untreated and stored at 10 or 21C. Damaged fruits were counted and classified as crushed, cut, bruised, abraded, and other injuries. Fruit injury was less dependent on whether the operation was a packing house or a field packing line than on the overall handling practices of the individual grower. In general, packing peppers in packing houses resulted in an increased number of bruises, whereas fruit from field packing lines had more abrasions. More open skin injuries resulted in greater fruit decay. In both years, fruits stored at 10C had less top rot than fruits stored at 21C. In 1992, they also had less pod rot. Dry and chlorinated lines often had equivalent rot problems.