Genetically Modified Crops: Assessing Safety

By Keith T. Atherton | Go to book overview

Chapter 10

Case study: virus-resistant crops

Hector Quemada


Squash and virus disease

Agricultural importance of cucurbits and squash

Squash (Cucurbita pepo L.) belongs to the Cucurbitaceae, a family of crops that is an important source of food throughout the world. While not as important as the cereals or oilseed crops, such as soybean, nor other vegetable crops such as potatoes and tomatoes, cucurbits are nevertheless grown on significant acreages worldwide. In 1998, cantaloupes and other melons were grown on 1 044 672 hectares, producing 17 764 188 metric tonnes of food; cucumbers and gherkins were grown on 1 567 389 hectares, producing 26 673 943 metric tonnes; while pumpkins, squash, and gourds were grown on 1 136 083 hectares, producing 14 169 983 metric tonnes (FAO, 1998). Cucurbit crops, including squash, are used for food in all regions of the world, but are also used for oil and other non-food uses, such as musical instruments or household implements.


Impact of virus disease on squash

Squash, like the other major cucurbit crops, is susceptible to infection by several viruses. The most damaging are cucumber mosaic virus (CMV), papaya ringspot virus watermelon strain (PRSV-W), watermelon mosaic virus 2 (WMV2) and zucchini yellow mosaic virus (ZYMV) (Provvidenti, 1990; Zitter et al., 1996; Fuchs et al., 1998). While the extent to which viruses cause economic damage in cucurbits, and squash in particular, is not well documented, the problem is extensive enough that diligent effort to breed squash resistant to CMV, PRSV-W, WMV2 and ZYMV has been a goal of breeders for many decades (Provvidenti, 1990).


Disease breeding in squash

Sources of genes for resistance or tolerance to viruses have been reported in various relatives of squash and in Cucurbita pepo itself. However, introducing useful levels of resistance to more than one virus into commercially acceptable cultivars has been difficult to achieve (Provvidenti, 1990; Table 10.1). While releases of zucchini-type and English marrow-type varieties carrying resistance to a single virus (CMV) has been achieved (Anonymous, 1992), breeding for multiple virus resistance has only

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