Plant Diseases - Nematodes

This time I’m researching nematodes, which are non-segmented round worms found in soil, water, and extreme environments such as deserts and ice fields. A few can be seen with the naked eye, but most are tiny and require magnification. For resources I’m using Essential Plant Pathology, information from my plant diseases course at Merritt College in Fall 2012, and Five Kingdoms. Keep in mind that most nematodes are beneficial – they aerate the soil, consume detritus, feed on bacteria and other small life forms, and circulate organic and mineral soil components. Others cause considerable damage to crops, turf, and plants in the landscape. Nematodes can be found in the San Francisco Bay Area.

Nematodes are categorized as Eukarya in the Animalia kingdom. About 10% of all nematodes are plant parasites, and require a living host (obligate parasites). They are aquatic and typically live, feed, and move in the soil. They use a specialized feeding structure—called a stylet—to penetrate plant tissue, probe, secrete proteins and polysaccharides, and ingest cellular contents. Most nematodes are migratory and move from cell to cell to feed (ectoparasites). Others are sedentary and remain embedded in a plant throughout their lifecycles (endoparasites); some endoparasites induce formation of specialized feeding sites, such as galls, where they live and feed. A few do not fit either of these categories.

The female nematode lays hundreds of hardy eggs (some species do not require male fertilization of the eggs). The eggs can exist in soil for years or decades, until the right environmental conditions exist for them to infect a plant. Their life cycle includes four juvenile stages. Nematodes molt, shedding the outside cuticle and part of the lining of the stylet, from stage to stage as they grow. Juveniles look like miniature adults through all stages (they do not undergo a metamorphosis from stage to stage).

Take a look at several nematodes; of special interest (1) views of the stylet at 57, 107, and 145 seconds, (2) a root rot nematode at 159 seconds, and (3) a needle nematode at 202 seconds: http://youtu.be/Qf8oGjqyXFc