Legume Management Research for VA Mycorrhizal Enhancement in Potato Production
Potato production is of major significance in the North Central region. A primary limiting factor
in potato production is the joint action of the Penetrans Root-Lesion Nematode (Pratylenchus
penetrans) and the Dahliae Wilt Fungus (Verticilium dahliae) resulting in a disease complex
frequently referred to as Potato Early Die (PED). Tuber yield losses to PED are often as high as
25-60 percent. PED is currently controlled through the use of nematicides, and to a lesser extent
crop rotation. There is a distinct need to develop improved procedures to protect potato (Solanum
tuberosum) form PED in commercial agriculture. The proposed project consists of laboratory and
field research, on-farm demonstrations, and industry communications designed to show that
specific legume management systems enhance colonization of S. tuberosum roots by VAM
(vesicular-arbuscular mycorrhizae), thereby increasing tolerance to P. penetrans and V.dahliae.
1) Develop legume management systems designed to enhance vesicular-arbuscular mycorrhizae
activity and sustain field-level potato production through protection against pathogenic
nematodes and fungi.
2) Use on-farm commercial potato production sites to demonstrate legume management to
control pathogenic nematodes and fungi.
3) Disseminate the results of the project to the Michigan and U.S. potato growers through the
Michigan Potato Industry Commission and National Potato Council
Soil samples were collected in the fall of 1991 from fields under different management
conditions at the Butler Potato Farm (Crystal Falls, Michigan) and Kitchen Potato Farm (Alba,
Michigan). The collections sites included new potato land, moderate PED risk soil, high PED
risk soil, and low-input soil. The samples were analyzed for diversity of VAM species, and
density of PED causal agents during the winter and spring of 1992. Specific clover and alfalfa
cultivars and other legume species were screened for VAM enhancement during 1992. Timing of
planting, length of growth period, and method of green manure incorporation were evaluated for
VAM enhancement under controlled conditions in 1992 and 1993. A greenhouse pathogenicity
study with indigenous VAM and a VAM research isolate of Glomus intraradix was used to
confirm the role of VAM fungi on the tolerance of S. tuberosum to P.penetrans and V.dahliae.
Potato tuber quality and yields at the Kitchen Farm were highest in the three-year crop rotation
and lowest when two consecutive crops of potatoes were grown. A single year in a rotation crop
resulted in intermediate tuber quality and yield. Similar results were obtained on the Butler farm.
Population densities of root-lesion nematodes and the Verticillium-wilt fungus were inversely
correlated with tuber yield. Rotations including Sudax, however, resulted in the poorest tuber
quality and yield, and the highest population densities of the Verticillium-wilt fungus.
Some of the results of the greenhouse studies did not appear to support the results of the on-farm
research components of the project. Four potato soils from the Kitchen and Butler Farms with
natural populations of the root-lesion nematode and Verticillium-wilt fungus were used in
greenhouse studies to evaluate the efficacy of nine crop rotations in the suppression of potato
early die. Root-lesion nematode population in subsequent potato crops increased in proportion to
the number of weeks of alfalfa or clover growth. This trend is less pronounced where the field
soil had been exposed to soil fumigants in previous years. The percent of plant survival increased
with increases in the number of weeks of alfalfa or clover. Both tuber weight and tuber number
decreased at three and six weeks for rotations of more than eighteen weeks of clover or alfalfa