Guest guest Posted July 12, 2004 Report Share Posted July 12, 2004 > 12 Jul 2004 14:11:58 -0000 > Two Rice Better than One > press-release > > > The Institute of Science in Society Science Society > Sustainability http://www.i-sis.org.uk > > General Enquiries sam Website/Mailing > List > press-release ISIS Director > m.w.ho > ======================================================== > > > Rice wars > > > Rice, the staple food crop for more than half the > world's > population, among them the poorest, is the current > target of > genetic modification, an activity that has greatly > intensified after the rice genome was announced two > years > ago (see " Rice is life " series, SiS 15, Summer 2002 > http://www.i-sis.org.uk/isisnews/sis15.php ). Since > then, > all major biotech giants are investing in rice > research. > > At the same time, a low-input cultivation system > that really > benefits small farmers worldwide has been spreading, > but is > dismissed by the scientific establishment as > " unscientific " . > This is one among several recent innovations that > increase > yields and ward off disease without costly and > harmful > inputs, all enthusiastically and widely adopted by > farmers. > > A war is building up between the corporate > establishment and > the peoples of the world for the possession of rice. > The > food security of billions is at stake, as is their > right to > grow the varieties of rice they have created and > continue to > create, and in the manner they choose. > > This extended series will not be appearing all at > once, so > look out for it. Fantastic Rice Yields Fact or > Fallacy? > http://www.i-sis.org.uk/RiceWars.php > Top Indian Rice Geneticist Rebuts SRI critics > http://www.i-sis.org.uk/TIRGRSRI.php > Does SRI work? > http://www.i-sis.org.uk/DSRIW.php > Corporate Patents vs People in GM Rice > http://www.i-sis.org.uk/CPVPIGMR.php > Promises and Perils of GM Rice > http://www.i-sis.org.uk/PPGMR.php > Two Rice Better Than One > http://www.i-sis.org.uk/TRBTO.php > > > ISIS Press Release 12/07/04 > Two Rice Better than One > ************************ > > Lim Li Ching reports on remarkable results from a > simple > experiment in China that combats rice disease and > increases > yields > > The sources for this article are posted on ISIS > members' > website http://www.i-sis.org.uk/full/TRBTOFull.php. > Details > here. > > Planting a diversity of crops instead of > monocultures can do > wonders. Thousands of Chinese rice farmers have > increased > yields and nearly eliminated the most devastating > disease - > rice blast fungus - without using chemical > fungicides or > spending more money. > > These farmers and extension workers in Yunnan > Province > collaborated with a team of scientists from Yunnan > Agricultural University, the Plant Protection > Stations of > Honghe Prefecture, Jianshui County and Shiping > County in > Yunnan Province, the International Rice Research > Institute > and Oregon State University in the United States to > implement a simple change in cultivation practice in > order > to control rice blast, a disease that destroys > millions of > tonnes of rice and costs farmers several billion > dollars in > losses each year. > > The area is prone to rice blast epidemics because of > its > cool, wet climate. The fungus that causes blast > disease, > Magnaporthe grisea, spreads through multiple cycles > of > asexual spore production during the cropping season, > causing > necrotic spots on leaves and necrosis (death) of the > rice > panicles. > > Instead of planting large stands of a single type of > rice, > as had been their usual practice, the farmers > planted a > mixture of two different kinds of rice: a standard > hybrid > rice that does not usually succumb to rice blast, > and a much > more valuable but lower-yielding glutinous or > 'sticky' rice > known to be very susceptible to the disease. Before > 1998, > 98% of rice fields in the area were monocultures of > the > hybrid rice varieties Shanyuo22 and Shanyuo63. The > glutinous > varieties, although highly valued, were planted in > small > amounts due to their low yields and vulnerability to > rice > blast. > > The experiment with mixed varieties dispersed single > rows of > glutinous rice between groups of four rows of hybrid > rice, > but at a rate sufficient to meet the local demand > for > glutinous rice. As rice is hand-harvested in Yunnan, > farmers > can easily separate the hybrid and glutinous grains, > which > are used for different purposes. > > In 1998, the first year of the trial, four different > > mixtures of varieties were planted over 812 > hectares, > comprising all the rice fields in five townships of > Shiping > County, Yunnan Province. The mixtures gave excellent > blast > control, such that only one foliar fungicide spray > was > applied. The study expanded to 3 342 hectares in > 1999, > encompassing all the rice fields in 10 townships of > Jianshui > and Shiping Counties. No fungicidal spray was needed > that > year. Farmers were so convinced of the benefits of > the rice > diversification program that the practice expanded > to more > than 40 000 hectares in 2000. > > The mixed rice fields were compared with control > monoculture > plots. The overall results showed that > disease-susceptible > rice varieties planted in mixtures with resistant > varieties > had 89% greater yield and blast was 94% less severe > than > when they were grown in monoculture. Both glutinous > and > hybrid rice showed decreased infection. > > Specifically, in 1998, panicle blast severity on the > > glutinous rice averaged 20% in monocultures, but was > reduced > to 1% when dispersed within the mixed populations. > Meanwhile, panicle blast severity on the hybrid > varieties > averaged 1.2% in monocultures, but was reduced to > varying > degrees in the mixed plots. Results from 1999 were > very > similar to the 1998 season for panicle blast > severity on > susceptible glutinous varieties, showing that the > effect of > mixed planting was very robust. Panicle blast > severity on > the less-susceptible hybrid varieties averaged 2.3% > in > monoculture in 1999, and was reduced to 1.0% in > mixed > plantings. This despite the fact that the hybrids > were > planted at the same density in mixed and monoculture > plots. > > The hypothesis for the reduced severity of blast > attack is > fairly clear for the disease-susceptible glutinous > rice. If > one variety of a crop is susceptible to a disease, > the more > concentrated those susceptible types, the more > easily the > disease will spread. The disease is less likely to > spread if > susceptible plants are separated by other plants > that do not > succumb to the disease and the distance between the > susceptible plants increased (a dilution effect). In > > addition, the glutinous rice plants, which are > taller and > rise above the shorter hybrid rice, enjoyed sunnier, > warmer > and drier conditions that discouraged the growth of > rice > blast. > > Disease reduction in the hybrid variety is more > difficult to > explain, but is possibly due to the taller glutinous > rice > physically blocking the airborne spores of rice > blast and/or > altering wind patterns. It is also likely that there > was > greater 'induced resistance' playing a part in > disease > suppression. Induced resistance occurs when > non-virulent > pathogens induce a plant defence response that is > effective > against other pathogens that would normally be > virulent on > the plant. Indeed, preliminary analysis of the > genetic > composition of pathogenic populations indicated that > mixed > fields supported diverse pathogen populations with > no single > dominant strain. By contrast, pathogen populations > in > monocultures were dominated by one or a few strains. > Hence, > the more diverse pathogen population of the mixed > stands may > have contributed to greater induced resistance in > the > plants, and in the longer term this increased > pathogen > diversity may also slow down the adaptation of > pathogens to > the resistant genes functioning within a given mixed > plant > population. > > Grain production per hill of glutinous varieties in > mixtures > averaged 89% more than when planted in monoculture. > As a > result, although glutinous rice in mixtures was > planted at > rates of only 9.2 and 9.7% that of monoculture in > 1998 and > 1999, respectively, it produced an average 18.2% of > monoculture yield. The higher yields are certainly > due to > the reduced severity of rice blast fungus, though > other > factors (for example, improved light interception) > may also > have contributed. Hybrids planted in mixtures, > despite > facing an increased overall plant density, > experienced grain > yields per hectare that were nearly equal to the > hybrid > monocultures. Thus, mixed populations produced more > total > grain per hectare than their corresponding > monocultures in > all cases. > > The mixed varieties of rice were also more > ecologically > efficient. It was estimated that an average of 1.18 > hectares > of monoculture cropland would be needed to provide > the same > amounts of hybrid and glutinous rice as were > produced in one > hectare of a mixture. Additionally, after accounting > for the > different market values of the two rice types, the > gross > value per hectare of the mixtures was 14% greater > than > hybrid monocultures and 40% greater than glutinous > monocultures. > > The scientists concluded that intra-specific crop > diversification is a simple, ecological approach to > disease > control, which can be extremely effective over a > large area > and can contribute to sustainable crop production. > > > > ======================================================== > > This article can be found on the I-SIS website at > http://www.i-sis.org.uk/TRBTO.php > > > If you like this original article from the Institute > of > Science in Society, and would like to continue > receiving > articles of this calibre, please consider making a > donation > or purchase on our website > > http://www.i-sis.org.uk/donations. > > ISIS is an independent, not-for-profit organisation > dedicated to providing critical public information > on > cutting edge science, and to promoting social > accountability > and ecological sustainability in science. > > If you would prefer to receive future mailings as > HTML > please let us know. If you would like to be removed > from our > mailing list at > > http://www.i-sis.org.uk/mailinglist/.php > ======================================================== > > CONTACT DETAILS > > The Institute of Science in Society, PO Box 32097, > London > NW1 OXR > > telephone: [44 20 8643 0681] [44 20 7383 3376] > [44 20 > 7272 5636] > > General Enquiries sam Website/Mailing > List > press-release ISIS Director > m.w.ho > > MATERIAL IN THIS EMAIL MAY BE REPRODUCED IN ANY FORM > WITHOUT > PERMISSION, ON CONDITION THAT IT IS ACCREDITED > ACCORDINGLY > AND CONTAINS A LINK TO http://www.i-sis.org.uk/ > > Quote Link to comment Share on other sites More sharing options...
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