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Arthur M. Richwine, Jimmy L. Tipton and Gary A. Thompson

Shoot cultures of Aloe, Gasteria, and Haworthia species were initiated directly from immature inflorescences. Explants placed on a modified MS medium containing 5.4 mm zeatin riboside initiated shoots within 8 to 12 weeks. Long-term shoot cultures were established and maintained on media containing either 5.4 μm zeatin riboside or 4 μm BA. Shoots easily rooted in vitro, and rooted plantlets were esablished in soil. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); 6-[4-hydroxy-3-methyl-but-2-enylamino]purine riboside (zeatin riboside).

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John Klingler, Irina Kovalski, Leah Silberstein, Gary A. Thompson and Rafael Perl-Treves

Resistance to cotton-melon aphid (Aphis gossypii Glover) segregated as a single dominant gene in a melon (Cucumis melo L.) mapping population derived from the cross `Top Mark' × PI 414723. Sixty-four F2-derived F3 families were used to map the aphid resistance locus, Vat, with respect to randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers. RFLP markers NBS-2 and AC-39 flanked Vat at distances of 3.1 cM and 6.4 cM, respectively. NBS-2 is homologous to the nucleotide binding site-leucine-rich repeat (NBS-LRR) superfamily of plant resistance genes. Another homolog of this superfamily, NBS-5, was positioned ≈16.8 cM from Vat, raising the possibility that Vat resides in a cluster of NBS-LRR paralogs. RFLP marker AC-8, which has similarity to plant lipoxygenases, was positioned at ≈5.5 cM from Vat. Monogenic resistance to A. gossypii has been identified in two sources of melon germplasm, Indian accession PI 371795 (progenitor of PI 414723) and Korean accession PI 161375. To test for an allelic relation between the genes controlling aphid resistance in these two distinct germplasm sources, melon plants of a backcross population from a cross between two resistant lines having Indian- or Korean-derived resistance were infested with aphids. At least 90 out of 92 segregating progeny were aphid resistant, suggesting that the same resistance gene, Vat, is present in both sources of melon germplasm.