Category: Breeding

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Biodiversity and rice pests

How should farmers deal with rice pests? Spray? Use resistant varieties? Or rely on bio-control ecosystem services?

Brown Plant Hopper Spraying is what many farmers do, to the detriment of their health and environment. It also makes the pest problem worse. Why? Because pesticides also kill the pests’ natural enemies, such as spiders. So you need to spray again, and again. Until the pests are pesticide resistant. This has led to huge outbreaks of brown plant hopper, like in Indonesia in the 1980s, which only stopped after most pesticides were banned. ((Brown plant hopper image from CSIRO.))

Use host plant resistance is what many researchers say. Sounds simple enough, and now there are GMO approaches to get that in different forms. Nature magazine recently had a piece ((Apologies for a post with many references to articles behind a paywall.)) about GM approaches to get insect resistant rice in China. ((Also see this paper by Huang et al. in Science and the critical responses.))

But not everybody agrees. The problem is that some of the major pests occur in large numbers and rely entirely on rice for their life cycle. Strong evolutionary pressure means that these species tend to quickly overcome host plant resistance. In the Nature article, KL Heong calls pest-resistant GM crops a short-term fix for long-term problems caused by crop monoculture and overuse of broad-spectrum pesticides. “Pests thrive where biodiversity is at peril, instead of genetic engineering, why don’t we engineer the ecology by increasing biodiversity?”

This week, in a letter to the editor of Nature, Settele, Biesmeijer and Bommarco also make a case for ecological engineering: the design and construction of ecosystems.

The nice thing about tropical rice is that there is not that much engineering needed to keep pests under control. This is my understanding of how it works:

  • Rule #1: do not kill the beneficial insects (avoid pesticides).
  • Rule #2: help the beneficial insects. For example, by providing ample organic matter to fields, you increase the population of harmless insects and with that the population of generalist predators (see below).
  • Rule #3, maintain a diverse landscape around the rice fields to support useful insects, such as parasitoids that, as adults, need nectar from flowering plants.

William Settle and colleagues studied rice bugs in Indonesia and summed their findings up like this:

By increasing organic matter in test plots we could boost populations of detritivores and plankton-feeders, and in turn significantly boost the abundance of generalist predators. We also demonstrated the link between early-season natural enemy populations and later-season pest populations by experimentally reducing early-season predator populations with insecticide applications, causing pest populations to resurge later in the season.

Irrigated rice systems support high levels of natural biological control that depends on season long successional processes and interactions among a wide array of species. Our results support the conservation of existing natural biological control through a major reduction in insecticide use, and an increase in habitat heterogeneity.

While it seems obvious that relying on and strengthening ecosystem services is the way to go, this is not what is happening. The brown plant hopper is coming back as a major problem, particularly in Vietnam and China. The response? Breeding & Spray, baby, spray.

It is tricky to generalize about agriculture and pests. There are always exceptions and special circumstances. And what if someone can make a rice plant that is truly immune to stem borers and plant hoppers. Well, some other insects would go after the available resources, but it could certainly be beneficial. Also, the biodiversity of insects in tropical rice fields, such as in Indonesia, is much higher than in China (probably largely because of the general relation between latitude and diversity, but perhaps also because of excessive pesticide use in China). So perhaps biocontrol ecosystem services are not as effective in China as in more tropical areas. We should find out.

And we should get serious about ecological engineering.

And not just in rice. Take this article that appeared in this week’s PNAS. It describes the need for maintaining landscape diversity in the USA, to support aphid control in soybeans by ladybugs.

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The hype goes on

“More food at lower cost.”

Now there’s a headline packed with potential. Alas, that’s all it has at the moment, potential. Not to denigrate the science of Angharad R. Jones — known to his pals as Harry — and colleagues at the University of Bristol. ((The full paper is in Nature Cell Biology.)) They’ve done some nifty research into what makes plant root hairs grow. It’s a complex study involving a computer model of where the plant hormone ought to be, and the bottom line seems to be that it isn’t where the researchers thought it would be.

Great. A deeper understanding of the development of root hairs is important. Root hairs, after all, are the basis of the plant’s uptake of minerals and water. But the press release goes well beyond that:

This new understanding will be crucial in helping farmers to produce food sustainably and to reduce fertiliser waste, which can cause severe damage to ecosystems.

I’ve written the odd press release myself, and I know how hard it can be to interest reporters in the small individual bricks that make up the building that is scientific understanding. But this kind of reporting is, I fear, going to lead inevitably to overinflated expectations and crushing disappointment.

If anyone notices.

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Orange revolution

Sweetpotatoes come in different colors and tastes (and sizes). The “yams” eaten in the United States are sweet and have orange and moist flesh. The staple of parts of Africa and the Pacific (and pig feed in China), is typically white-fleshed and not very sweet nor moist (notwithstanding variations like this purple variety.)

Anyway, the orange fleshed sweetpotato is stacked with beta-carotene, the stuff you need to eat for your body to make vitamin A. Many poor people have vitamin A deficiencies, which leads to stunted growth and blindness. So why don’t the poor sweetpotato eaters eat orange fleshed varieties? In part because they simply do not have them, or know about their health benefits. In part because they do not grow well in Africa (decimated by pests and diseases). And also because they do not taste right: too sweet for a staple.

The International Potato Center and partners have been trying to fix all that. Now they have made a nice video about getting orange-fleshed sweetpotatoes into the food-chain in Mozambique. The orange revolution:

https://vimeo.com/2278794

I wonder if they also promote mixing more sweetpotato leaves into the diet — even of white fleshed varieties. The leaves are a very good source of micro-nutrients, including beta-carotene! More fodder for the biofortification discussion.

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Nibbles: Early diet, Rice, Veggies, Barley, Research, Taiwan, Coffee trade