Healthy soil and sustainable growing

["Lawrence F. London, Jr." <lfl@intrex.net>]

"Lawrence F. London, Jr." <lfl@intrex.net>

<http://www.sciencenews.org/articles/20040710/fob5.asp>
Week of July 10, 2004; Vol. 166, No. 2 , p. 21
Plastic vs. Plants: Mulch method changes tomato's gene activity

Susan Milius

A suite of at least 10 genes in a tomato plant behaves differently depending 
on the farmer's mulch-and-fertilizer routine, according to an
unusual analysis.

MULCH MATTERS. Two fields of Sunbeam tomatoes planted at the same time and 
photographed on the same day. In a season with adequate rainfall,
tomatoes mulched with black plastic and given standard fertilizer (above) 
developed more leaf diseases and aged faster than the same variety
planted in mown vetch and given half the fertilizer (below).
Dave Clark

Earlier work showed that when researchers mulch with a layer of mown vetch 
instead of the conventional black plastic, tomato plants live
longer and develop less fungal disease, says Autar Mattoo of a Department of 
Agriculture laboratory in Beltsville, Md. He and his colleagues
now report insight into the underlying plant chemistry.

Among the genes that kick into higher activity in vetch-mulched fields are 
two for plant defense and two for regulation of aging, the
researchers say in an upcoming Proceedings of the National Academy of 
Sciences. "This kind of molecular analysis had not been done before,"
says Mattoo.


Dave Clark

The vetch system has been around for decades among farmers practicing 
environment-friendly agriculture. Over the winter, the farmers grow
hairy vetch, a member of the bean family, and they mow it in the spring. They 
then set out tomato plants in the matted vetch, which
discourages weeds and boosts nutrients in the soil.

Beltsville researchers compared vetch-mulched fields given half the normal 
dose of commercial fertilizer with plastic-mulched fields given a
full dose of fertilizer. In years with sufficient rainfall, the vetch-treated 
fields yielded a Sunbeam tomato crop bigger than that of
fields receiving conventional treatment. Although the plastic mulch provided 
the crop a little sooner, the vetch mulch offered other
benefits, including reduced erosion, decreased signs of fungal disease on 
leaves, and delays in plant aging. These benefits appeared during
two seasons but not in a third, when there was a severe drought.

To search for a mechanism behind the disease and aging benefits, Mattoo, 
Vinod Kumar of the same lab in Beltsville, and their colleagues
studied proteins and genes in tomato plants grown in the two 
mulch-and-fertilizer systems. Among their analyses, the researchers used a
technique that highlights differences in gene activity.

Among the genes that kicked into higher activity in vetch-mulched plants are 
a gene for chitinase, an enzyme that chews up the cell walls of
attacking fungi, and a gene for osmotin, another defensive compound. The 
researchers also found extra activity for receptors for cytokinins.
These plant hormones, which travel from the roots to the rest of the plant, 
are regulators of aging.

Mattoo has many ideas to explain the difference in the effects of the two 
crop-growing methods. For instance, he points out that nutrients
can influence gene activity and that vetch-mulched tomatoes typically produce 
especially robust root systems that take up soil nutrients
efficiently.

Plant physiologist Thomas Sinclair of the USDA in Gainesville cautions that 
the patterns of gene activity reported so far are "correlations,
not cause and effect." He adds that whatever the physiology turns out to be, 
"I'll guarantee you it's going to be very complicated."

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