Improved maintenance of the tomato - like Solanum spp . by grafting   Chetelat, R . T . and J . P . Petersen C . M . Rick Tomato Genetics Resource Ctr . , Dept . of Vegetable Crops, Univ . of California, Davis, CA   95616 We have struggled over the years to reproduce the tomato - like Solanum species our collection .   S . juglandifolium is diffi in cult because some accessions refuse to flower under our greenhouse conditions, even during short - day regimes which induce other sensitive species .   Its close cousin S . ochranthum flowers somewhat more readily, but only after growing so tall that it becomes difficult to handle .   Finally, the xerophyte S . sitiens is hypersensitive to soil - borne fungal pathogens, usually brought on by over watering or transplant stress .   As a result, many plants succumb before seed can be harvested, resulting in inadvertent selection and loss of genetic diversity in subsequent generations .   Our repeated attempts to ameliorate this problem by careful watering, applications of fungicides, or use of specialized soil mixes have met with limited success .    Each of these challenges can be overcome by grafting the nightshades onto a tomato rootstock .   Rick (TGC 37:62) used L . esculentum cv . VF36 as a graft rootstock to promote flowering in S . juglandifolium .   However, during the time it takes to reproduce this species (up to ~ 2 years), rootstocks would eventually lose vigor or die altogether due to attack by Phytophthora root rot and other diseases .   We therefore tested the interspecific hybrid F 1 L . esculentum cv VF36 x L . pennellii LA0716 as a potential graft rootstock .   This genotype has several advantages for grafting applications .   First, the hybrid is amazingly vigorous in its vegetative growth, as anyone who has had the misfortune to include it in a field trial can attest (a single plant will quickly overwhelm rows on either side) .   Secondly, the L . pennellii parent contributes dominant resistances to multiple races of Fusarium wilt .   As a result, roots of the hybrid are either resistant to or can ‘outgrow’ our common soil - borne diseases, and plants can be maintained indefinitely in pot culture .   Thirdly, the hybrid has wide graft compatibility, not only with the Solanum spp . in question, but also with more distantly related Solanaceous crops, such as eggplant ( S . melongena ) and pepper ( Capsicum spp . ) .   Finally, L . pennellii and its hybrid with tomato are daylength insensitive, and flower continuously throughout the year, with relatively few leaves between successive inflorescences (sympodial index = 2 in L . pennellii ) .   Although the hybrid has an annoying tendency to sprout adventitious shoots, these are easily distinguished from scion branches and pruned off .    Standard cleft type grafts were made when the rootstock was at the ~4 - 5 true leaf stage, using stems of roughly the same diameter, from each of the three Solanum spp .   Graft unions were wrapped with Nescofilm, and scion branches were pruned to several axillary buds, then enclosed in a Ziploc plastic bag for 10 - 14 days .   Only a small proportion (<10%) of grafts failed on the first attempt, generally due to a poor match in stem diameter/age, or Botrytis infection .   Both graft partners recovered readily from wounding, with shoots of the Solanum spp . becoming woody and strong, and growing vigorously .   For S . juglandifolium (LA2120 and LA2788) and S . ochranthum (LA2166 and LA2682), grafts were made starting

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