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Jayasankar Subramanian, Richard E Litz, and Raymond J. Schnell

Anthracnose, caused by Colletotrichum gloeosporioides, is the most serious production and postharvest problem of mango. Most mango cultivars are highly susceptible to this disease. Embryogenic nucellar cultures of two cultivars, `Hindi' and `Carabao', were recurrently selected with either the purified phytotoxin or the crude culture filtrate produced by the fungus. Mycelium growth was suppressed in dual cultures involving the recurrently selected lines. Enhanced extracellular production of proteins was observed in the embryogenic cultures and in regenerants, including a newly expressed acidic chitinase isozyme (`Hindi') and greater expression of two other chitinase isozymes (`Hindi' and `Carabao'). Activity of α-1,3-glucanase was also substantially increased in the recurrently selected lines. Resistant lines were characterized using RAPDs on the basis of polymorphisms generated by eight different primers. In most cases, the differences involved the absence of RAPD markers in resistant lines.

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Dineshkumar Selvaraj, Sherif Sherif, Mohd Sabri Pak Dek, Gopinadhan Paliyath, Islam El-Sharkawy, and Jayasankar Subramanian

European plum fruit (Prunus domestica) are normally blue-black to dark purple. However, some genotypes remain green/yellow after ripening. We hypothesized that in such genotypes anthocyanin biosynthesis is genetically disturbed. To examine this hypothesis, six european plum genotypes with diverse fruit colors were investigated for the expression pattern of several anthocyanin biosynthetic genes (ABGs)—e.g., phenylalanine ammonia-lyase, chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), anthocyanin synthase (ANS), and UDP-glucose:flavonoid 3-O-glucosyltransferase 1 and 2 (UFGT 1 and 2). Expression profiles indicated that ABGs, especially Pd-CHS and UFGT 2, were significantly downregulated in the green/yellow fruit compared with the dark-purple fruit. Furthermore, the quantification of total polyphenols and individual flavonoid compounds showed substantial differences between the off-colored and the purple genotype. To further examine the contribution of each of the ABGs in color development, the open reading frame (ORP) of Pd-CHS, Pd-DFR, Pd-ANS, and Pd-UFGT 2 was ectopically expressed in tobacco (Nicotiana tabacum). The characterization of transgenic plants showed that the petals of plants expressing Pd-CHS were darker in color and had higher anthocyanin content than control or even other transgenic types, suggesting the significant contribution of CHS in determining anthocyanin production levels and hence fruit coloration. The results of this study provides better understanding of color development in european plum, which can be rewarding in developing european plum cultivars with desired colors through classical or modern breeding tools.