Laboratory Report

By: Robert D Raabe

Robert D Raabe is Professor Emeritus of Plant Pathology at University of California, Berkeley. He introduced a faster method of…

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Destruction of Phenolic Resins

Phenolic resins are produced in the US at an annual rate of 2.2 million metric tons. They are used as industrial adhesives for products such as exterior plywood, Oriental strawboard, density fiberboard, plastic trim on car bodies, and plastic containers that hold air filters. They are resistant to attack by fungi and termites and are not biodegradable. They also cannot be melted or remolded, so most of them end up in landfills. Researchers in Wisconsin questioned whether lignin degraders, such as white rot fungi, could degrade the resins, which have a molecular structure similar to lignin. After trying several white rot fungi and a brown rot fungus (which attacks cellulose), they found one fungus (Phanerochaete chrososporium) that was able to break down the resins in a short time to a water-soluble material, from which the constituents of the resins could be recovered. Environmental Science and Technology 40: 4196-4199.

 

Plant Volatiles Affecting Plants

It is known that plant volatiles aid insect herbivores and their natural enemies in plant location, and in identity and condition. Although it has been suggested that similar volatiles can also aid plants, there has been little proof until recently. Researchers in Pennsylvania began working with dodders, parasitic flowering plants that lack chlorophyll and belong to the morning glory family; dodders obtain their nutrients by attaching to the vascular systems of their host plants. They are quite detrimental, ranking among the top ten weeds by the USDA. Dodder seeds germinate in the soil but have limited energy reserves so must contact a host plant in a few days or die. The research revealed that dodder seedlings were attracted by volatile clues from nearby tomato seedlings. They were not attracted to artificial plants. They also were attracted to tomato plant volatiles in the absence of the plants, but not to the solvents used in extracting the volatiles. The researchers found that volatiles from impatiens and wheat also affected dodder growth, but that wheat elicited a compound that was repellant to the dodder. It is known that wheat is not a good host for dodder; when tested, dodder most frequently selected tomatoes over wheat. Science 313 No. 5795: 1964-1967.

Soybean By-products

USDA researchers at Beltsville, Maryland, have found that soybeans can be used for several unusual products. One of the new giant soybeans, which grows to seven feet tall, was found to be incredibly sturdy in the field, seldom being knocked down flat by the winds as some selections might be. Its stalks, which are the size of tree saplings, have cellulose fibers as strong as those in pine 2 × 4s. Thus, the crop has potential for use in wood products such as particle-board. Other giant forms are less sturdy because their cellulose is weaker. It has been found that soil microorganisms can break down these stems, making them potentially useful for ethanol production. Because soybeans are legumes, they can also fix atmospheric nitrogen, resulting in energy conservation by reducing the need to manufacture supplementary nitrogen. Agricultural Research 54(11, 12): 9.

Submergence of Rice Seeds

Seeds of most rice cultivars cannot survive more than a week of submergence. This constraint is a concern in South and Southeast Asia where it impacts, principally, the poorest farmers in the world. Losses amount to one billion dollars annually. Researchers in California, studying the genetics of rice, found three genes involved in a seed’s tolerance of submergence. Two of the genes are found in most of the cultivars, but the third one, though equally important, is found in only a few cultivars. By selective breeding, this gene was put into the widely grown cultivars; it was found that the new varieties not only maintained their high yield and other good qualities, but also were tolerant of submergence. Nature 442: 705-708.

Dwarfing Peach Trees

The dwarfing of fruit trees eases such tasks as pruning, thinning, spraying, and harvesting, thus resulting in high-grade fruits at a lower cost. In stone fruits, the lack of suitable dwarfing rootstocks is a limiting factor. Although girdling of the bark has been successful in the dwarfing of apple trees, it had not been tried on peach trees until researchers in Japan experimented with it. They found that a partial ringing of peach cultivars that had been grafted on strong wild rootstocks produced dwarf trees. Ringing was done so that a two-millimeter bridge of bark was left on the trees (ninety-six percent was ringed). Ringing weekly, every two weeks, or monthly was more effective than ringing only once. (Complete ringing resulted in the death of the trees.) This method can be used to dwarf fruit trees even when there are no dwarfing rootstocks available. Scientia Horticulturae 110: 38-43.

Marigolds and Nematode Control

Marigolds (Tagetes erecta and other species) have been shown to control rootknot nematodes as well as root-lesion nematodes. This has been successful when the marigolds were planted as intercrops or as rotation crops. However, both methods reduce crop yields because of the need to set aside productive land for the marigolds. Researchers in India and Great Britain used cold water extracts of T. erecta as a drench on container-grown tomato plants in a planting mix (equal parts sterilized soil, sand, and farmyard manure) that had been infested with the root-knot nematode (Meloidogyne incognita). They found that whole plant extracts from forty-day-old, pre-flowering plants gave better control than those from seventy-day-old, post-flowering plants; both were more effective in giving control than either stem or root extracts. Plant growth and fruit yields were comparable to those from plants treated with a commercial nematocide. Crop Protection 25: 1210-1213.