Comparative Virus Resistance and Fruit Yield of Transgenic Squash with Single and Multiple Coat Protein Genes

Abstract

Five transgenic squash lines expressing coat protein (CP) genes from cucumber mosaic cucumovirus (CMV), zucchini yellow mosaic potyvirus (ZYMV), and watermelon mosaic virus 2 potyvirus (WMV 2) were analyzed in the field for their reaction to mixed infections by these three viruses and for fruit production. Test plants were exposed to natural inoculations via aphids in trials simulating the introduction of viruses by secondary spread from mechanically infected susceptible border row plants. Plants of transgenic line CZW-3 expressing the CP genes from CMV, ZYMV, and WMV 2 displayed the highest level of resistance with no systemic infection, although 64% exhibited localized chlorotic dots which were mainly confined to older leaves. CZW-3 plants had a 50-fold increase in marketable yield compared to controls and the highest predicted cash returns. Plants of transgenic line ZW-20 expressing the CP genes from ZYMV and WMV 2 displayed high levels of resistance to these two potyviruses, but 22% became infected by CMV. However, ZW-20 plants provided a 40-fold increase in marketable yield relative to controls and good estimated cash returns. Three transgenic lines expressing single CP genes from either ZYMV (line Z-33), WMV 2 (line W-164) or CMV (line C-14) developed systemic symptoms similar to those of controls but showed a delay of 2 to 4 weeks before the onset of disease. Plants of transgenic line Z-33 were highly resistant to ZYMV but not to WMV 2 and CMV. Interestingly, Z-33 plants had a 20-fold increase in marketable yield compared to controls and some predicted cash returns if market sale prices were high. This study indicates that virus-resistant transgenic lines are economically viable even if they are affected by viruses other than those to which they are resistant.

In vitro organogenesis in watermelon cotyledons

“…Although a high number of multiple shoot buds apparently formed on the explants, very few buds were found when a histological study of cultures was done (Figure 1 h-i), in a similar way to the one reported for other cucurbit species (Gaba et al, 1999;Stipp et al, 2001). Adventitious shoots developed directly from the explant epidermal and subepidermal layers, without callus formation.…”

“…Protuberances with trichomes (Figure 1 j) which do not develop into buds were formed, indicating that these structures could be leaf primordia. Structures from which only leaves are developed have been described in cucurbit organogenesis (Gaba et al, 1999;Stipp et al, 2001;Yalcin-Mendi et al, 2003). This explains the apparently large number of buds observed during induction, resulting in a low number of plants after transfer to elongation medium.…”

“…This method has been used to develop resistance to cucurbit potyviruses in different cucurbit species (Tricoli et al, 1995;Fuchs et al, 1998;Compton et al, 2004). However, a breeding program associated to biotechnological tools depends upon the development of an efficient in vitro plant regeneration system.…”

Movement of coat protein genes from a commercial virus-resistant transgenic squash into a wild relative

“…Since the CZW-3 plants used as male parents were hemizygous for the CP and nptII transgenes, transgenic F1 hybrid plants were identified by detecting the expression of the NPT II protein by enzyme linked-immunosorbent assay (ELISA) as described previously (Fuchs and Gonsalves, 1995;Fuchs et al, 1998;Tricoli et al, 1995). No apparent differences in plant morphology, vigor and fruit production were observed between transgenic and nontransgenic F1 segregants in the greenhouse (data not shown).…”

“…Transgenic line ZW-20 which expresses the coat protein (CP) genes of Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV), and is resistant to these two viruses (Fuchs and Gonsalves, 1995;Tricoli et al, 1995) received exemption status in 1994 (Medley, 1994). Transgenic line CZW-3 which expresses the CP genes of Cucumber mosaic virus (CMV), ZYMV, and WMV, and is resistant to these three viruses (Fuchs et al, 1998;Tricoli et al, 1995) received exemption status in 1996 (Acord, 1996). Also, wild relatives of cultivated squash, including C. pepo ssp.…”