Bacterial infection causes fungal resistance

Some root colonizing bacteria have been found to have beneficial effects on plant growth, and have thus been dubbed plant growth promoting rhizobacteria (PGPR). Now Indian researchers have grown pigeonpea with and without a couple of different strains of PGPR, and also with and without rhizobium infection, and have then infected the plants with the fungus that causes wilt.1

It turns out that pigeonpea plants infected with either PGPR or rhizobium developed “induced systemic resistance” to the fungus. But the resistance was actually best when both were present. I found this pretty amazing, but actually some googling reveals that it’s not that weird. It may have something to do with the increased levels of phenols in the leaves of bacterized plants. Or the reduced production of fusaric acid by the pathogen. In any case, “the results promise the combined use of PGPR and rhizobia for induction of systemic resistance against fusarial wilt in pigeon pea.” They are also another pretty amazing example of the interactions among agrobiodiversity.

  1. S. Dutta, A.K. Mishra and B.S. Dileep Kumar. Induction of systemic resistance against fusarial wilt in pigeon pea through interaction of plant growth promoting rhizobacteria and rhizobia. Soil Biology and Biochemistry, In Press, Uncorrected Proof, Available online 11 October 2007 []

The Cretaceous roots of agriculture

A comment on a long but fascinating post on yeast genetics and evolution at The Loom sent me to a New Scientist article from a couple of years back which is perhaps more immediately relevant to our agricultural biodiversity focus here.

Some time in the distant past Saccharomyces cerevisiae, to give it its full name, developed a chemical trick that would transform human societies. Some anthropologists have argued that the desire for alcohol was what persuaded our ancestors to become farmers and so led to the birth of civilisation.

The article goes on to describe how brewer’s yeast evolved its somewhat surprising abilities. It turns out that its peculiar habit of carrying out anaerobic respiration even in the presence of oxygen — at a steep energetic cost, and resulting in the production of what is usually a poison, alcohol — dates back to an accidental duplication of its genome back in the Cretaceous. Eighty million years ago later, bakers and brewers are daily taking advantage of a genetic mistake that took place in a microscopic fungus when dinosaurs ruled the Earth. Isn’t agrobiodiversity wonderful?

Roman antibiotics

Also from Tangled Bank comes news of a study looking at the evidence for various infectious diseases from the skeletons of people killed at Herculaneum by the eruption of Vesuvius in 79 AD.1 Among the diseases was brucellosis, evidence for which was also gleaned from the carbonized cheeses found at the site. Herculaneum was apparently famous for its goat cheeses, which seem, however, to have been badly infected. Which is all amazing enough. But one of the commenters on the article points to another paper which adds a twist to the story.

It seems the inhabitants of Herculaneum, despite their brucellosis and tuberculosis, were relatively free of non-specific bone inflammations. And that may be because:

Pomegranates and figs, consumed by the population, were mainly dried and invariably contaminated by Streptomyces, a bacterium that produces natural tetracycline, an antibiotic.

Is there similar evidence from contemporary populations of the protection conferred by natural antibiotics?

  1. That’s the one that also destroyed Pompeii, though in a somewhat different way. []

Fungal agricultural biodiversity

More today about fungi as important constituents of agricultural biodiversity. Following the recent post on the microsymbiotic Frankia, I ran across a couple of papers on other fungi and their interactions with crop plants in agricultural systems. 

First, there’s Trichoderma. According to a recent review in Soil Biology and Biochemistry1:

Trichoderma spp. are among the most frequently isolated soil fungi and present in plant root ecosystems. These fungi are opportunistic, avirulent plant symbionts, and function as parasites and antagonists of many phytopathogenic fungi, thus protecting plants from disease. So far, Trichoderma spp. are among the most studied fungal BCAs [bio-control agents] and commercially marketed as biopesticides, biofertilizers and soil amendments. Depending upon the strain, the use of Trichoderma in agriculture can provide numerous advantages: (i) colonization of the rhizosphere by the BCA (“rhizosphere competence”) allowing rapid establishment within the stable microbial communities in the rhizosphere; (ii) control of pathogenic and competitive/deleterious microflora by using a variety of mechanisms; (iii) improvement of the plant health and (iv) stimulation of root growth.

Then there’s arbuscular mycorrhizal fungi (AMF). Another paper2 in the same journal suggests that different maize genotypes had quite different effects on the AMF population in the soil in which they were grown, stimulating “their own adapted phylogenetic AMF subgroups.” According to the authors:

Several new sets of data obtained in this way would be necessary to have a significant view of the actual beneficial interactions between rhizospheric microorganisms and plant roots; but we are confident that such an effort will lead to the definition of new criteria for the rapid breeding of sustainable varieties.

  1. Francesco Vinale, Krishnapillai Sivasithamparam, Emilio L. Ghisalberti, Roberta Marra, Sheridan L. Woo and Matteo Lorito, Trichoderma-plant-pathogen interactions. Soil Biology and Biochemistry. In Press, Uncorrected Proof. []
  2. Christine Picard, Elisa Baruffa and Marco Bosco, Enrichment and diversity of plant-probiotic microorganisms in the rhizosphere of hybrid maize during four growth cycles. Soil Biology and Biochemistry. In Press, Uncorrected Proof. []

Frankia and Alnus

There’s a lengthy review of an interesting-sounding book — People and Forests: Yunnan Swidden Agriculture in Human-Ecological Perspective1 — in the latest Agriculture, Ecosystems and Environment (though the book seems to have been published in 2001). You do need a subscription, but that turned out to be a blessing in disguise, because in an effort to get around the problem I did some googling, and that not only revealed a very similar review (I know because I had access to the AEE piece at work) by the same person2. It also led me to a resource I hadn’t come across before: People, Land Management and Ecosystem Conservation (PLEC) News and Views.

The March 2004 issue, which includes the book review, is devoted to “agrodiversity.” Here’s an excerpt from the introduction, by Miguel Pinedo-Vasquez, PLEC Scientific Coordinator (at the time), which certainly struck a chord:

Smallholder agrodiversity strategies have proved to be effective in dealing with widespread declines in the value of agricultural products, yet they continue to be underutilized by most programmes that aim to reduce rural poverty, environmental degradation, erosion of biological diversity, and other problems affecting rural communities.

Here’s more about PLEC from the website of the Department of Anthropology of the Australian National University:

PLEC is a global network, set up by the United Nations University in 1992. From 1998 until 2002 it was funded by the GEF through UNEP. It brings together over 200 professionals, including more than 130 scientists and researchers, together with 190 skilled expert farmers, and 180 undergraduate and graduate students. PLEC members work out of 65 institutions in Brazil, China, Ghana, Guinea, Jamaica, Kenya, Mexico, Papua New Guinea, Peru, Thailand, Tanzania, Uganda, Britain, the United States and Australia. From 1992 until 2002 it was coordinated scientifically by Em. Prof. Harold Brookfield, who is now Senior Adviser.

Conservation through agriculture underpins PLEC’s approach to conserving and utilising biological diversity. Most biodiversity projects relate to protected areas or crop plants alone. PLEC is unique still in its strong and pervading management approach to biodiversity in the context of the livelihoods and social organization of smallholder farmers. Through generations of innovation and experiment, they have nurtured a great diversity of plants and animals, both wild or domesticated, and accumulated rich knowledge of the managed biodiversity.

PLEC also has its own website, where you can subscribe to an electronic list.

Anyway, back to the book about swidden cultivation in Yunnan which started all this. One of the reasons the review caught my attention was the mention of the use of Alnus nepalensis in local agroforestry systems, and in particular the description of that tree as a nitrogen fixer. I had totally forgotten about the phenomenon of “alder-type” actinorhizal symbiosis between some plants and fungi of the genus Frankia. Fungi are agricultural biodiversity too!

  1. By Yin Shaoting, professor of anthropology at Yunnan University in Kunming []
  2. Prof. Harold Brookfield of the Australian National University []