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Effects of the okra leaf (OL) mutant of cotton on plant and agronomic traits, and its interaction with insect pests are reviewed. While a number of favourable effects e.g. reduction of bollrot, earliness of maturity have often been noted, only in Australia has there been widespread use (circa 50% of total Australian cotton plantings over the last eight years) of OL cultivars. This commercial acceptance and success of OL varieties in Australia is ascribed to a number of factors. The Australian-bred OL varieties (known as Siokras) have a high yield and quality potential and are resistant to bacterial blight. OL provides some resistance to bollworm and mite pests and finally Australian farmers are not prejudiced against OL’s unconventional appearance.
A questionnaire survey of Australian cotton consultants provided insights into commercial experiences and attitudes to OL varieties and their advantages and disadvantages. The survey revealed OL is well regarded commercially with many consultants citing better pest control, often accompanied by saving of insecticides. Other favourable features included earliness, ability of OL to recover from setbacks such as hailstorms and high yielding ability. Disadvantages included susceptibility to Verticillium wilt and high trash content at harvest resulting in reduction of grade.
It is concluded that in Australia at least, OL is a beneficial plant characteristic. Susceptibility of the Siokra varieties to Verticillium wilt is being overcome by breeding while a gene for glabrousness of leaves and stems is being incorporated to decrease trash levels at harvest and to enhance their resistance to bollworms and mites.
I believe that, viewed as a grand experiment, the Australian experience has conclusively shown that OL cottons can be bred that are commercially at least the equal for yield and intrinsic quality of NL cottons. Further, under Australian conditions, OL cottons have a HPR advantage over NL while their earlier maturity is also an advantage. However against these positive features there is an offsetting trend for lower grades associated with mechanically picked OL crops.
On balance I believe that OL cottons have “paid their way” in Australia where there is considerable concern about environmental contamination from the application of insecticides to cotton crops. Although OL cottons have only enabled modest reductions in insecticide usage and hence have had relatively small economic benefits they have helped the industry present a “greener” image to the wider community by showing that it is exploring all avenues of reducing spraying.
The response by consultants to the question of what proportion of area they would sow to OL whereby most consultants stated they would prefer a greater proportion of OL than NL crops (Table 3) if there were no yield or quality difference between leaf shapes shows that OL is indeed valued in commercial cotton circles.
We are also seeking to develop glabrous (ultra-smooth) OL cottons. This combination enhances HPR effects against both Heliothis and mites (Thomson et al., 1987; G. Fitt, L. Wilson, pers. comm.), and we expect (from experience with glabrous, frego bract cottons (Thomson, 1987)) will also help reduce trash content and thereby enhance the grade of OL cottons.
Finally the successes achieved with OL in Australia should encourage renewed attempts by other countries to develop their own adapted, productive OL cottons. For example boll rot is presumably still as serious a problem in Louisiana and other nearby states in the USA as it was when Jack Jones first started in the sixties on his quest to reduce its severity by the development of OL cottons. Again white flies have become a major threat in many countries. Surely this is another situation where OL can be used to advantage. But, breeders beware! For OL cottons to be acceptable to cotton producers they must be at least the equal of their NL competitors in yield and quality even in those seasons and locations when the environmental stress favouring OL, be it boll rot or white flies, or mites on whatever, is absent. Indeed to break down prejudices and to make up any grade loss associated with the mechanical picking of OL, such cultivars, at least initially, probably need to be discernibly better than their NL competitors.