UPDATE: RECENT RESEARCH DEVELOPMENTS AT TEXAS A&M-KINGSVILLE CITRUS CENTER IN WESLACO

(KINGSVILLE, December 20, 1996)-- Research underway at the Texas A&M-Kingsville Citrus Center at Weslaco shows promise for protecting the Rio Grande Valley citrus industry from potentially devastating virus and insects.

Promising findings on virus-resistant rootstocks, success in establishing a parasite that may biologically control the citrus leafminer insect, progress in developing virus-free citrus budwood, and the beginning of an Israeli cooperative effort to research potassium nutrition of citrus trees are the latest research developments announced by the Citrus Center.

"The Citrus Center is ready to give preliminary recommendations to Valley citrus growers about alternative virus-resistant rootstock for propagating citrus trees," reports Dr. Dariusz Swietlik, assistant center director and professor at the A&M-Kingsville Citrus Center and the Texas A&M Agricultural Research and Extension Center at Weslaco. "Presently-used sour orange rootstock in Valley orchards is susceptible to the tristeza virus, a deadly citrus disease."

Swietlik's research work looks at alternative rootstocks which not only are tristeza-resistant but also produce desirable characteristics such as superior fruit quality, large fruit size, and high yields.

The scientist has received a $7,000 grant from the Texas Citrus Producers Board for continuing development of an alternative rootstock. Grafting citrus varieties on rootstocks improves the quality of citrus fruit and the amount of fruit produced per acre. It also makes citrus trees more resistant to disease organisms and adverse soil conditions such as high salinity and poor soil aeration.

Another recent research outcome, developed by entomologist Dr. J. Victor French, is the biological control of citrus leafminer. French successfully established an exotic parasite, Ageniaspis citricola, which can control the leafminer. He was able to observe parasitism of citrus leafminer by Ageniaspis citricola in release-site trees. (Parasitism is the injury and destruction of the host organism, the citrus leafminer, as parasites feed on it.) The leafminer migrated to Rio Grande Valley orchards two years ago. "This research is of high importance for the practical control of this very destructive pest of citrus," said Swietlik.

The Texas Citrus Producers Board has awarded $8,800 for further work on biological control of this and other citrus insects to professor French and Dr. Jesusa Legaspi of the Texas Agricultural Experiment Station in Weslaco.

"Dr. Mani Skaria has worked this past year, under a grant from the U.S. Department of Agriculture, to survey orchards in the Valley and citrus trees in backyards of homes in Corpus Christi and Houston to find the tristeza virus," said Swietlik. "It looks promising that the USDA will continue Skaria's research funding for the next year."

Skaria, an associate professor of plant pathology, and a British graduate student, have worked on new methods of identifying another citrus virus that is called tatterleaf virus. Caroline Herron made her work on the tatterleaf virus a part of her thesis for a master's degree with the University of Bristol in England. Skaria directed her research, and the USDA provided funding.

The plant pathologist has been awarded $41,000 for the upcoming year to develop virus-free budwood. The research funding comes from the Texas Citrus Producers Board who has supported his research on budwood since 1993.

"Budwood is used to propagate citrus trees. Skaria will be 'cleaning' this budwood so that it doesn't contain viruses," explained Swietlik. "Budwood is cleaned thru a technique called shoot-tip grafting."

A one-year grant of $25,000 to Swietlik from the Texas Israeli Exchange Program, will be used to study how potassium nutrition affects grapefruit size. Swietlik will work with Drs. Yair Erner and Oded Sagee, Israeli researchers from the Israeli Ministry of Agriculture, to conduct complementary experiments on potassium nutrition under different environmental conditions found in South Texas and the arid climate of the Middle East.

The Weslaco and Israeli scientists' efforts will be aimed at increasing the size of citrus fruit. The research program is administered by the Texas Department of Agriculture. The Texas grant is being matched by the Israeli government.

Housing facilities for graduate students and visiting scientists were completed in July at the Center. "We have two graduate students now, and this housing enhancement will help us develop a stronger graduate student program," said Swietlik.

Renovation is currently in progress on the Center's main building and a nearby classroom building. Old floors are being rebuilt. Twenty-year-old carpeting is being replaced as well. The work is expected to be completed by March 1997.

Swietlik predicts "a better year of returns for our growers this year. We think that the fruit quality is better, and we will have higher yields, especially in oranges. This means more oranges per acre of land.

"But we remain concerned about our water supplies. We are in the fourth year of drought; we're not rationing water yet, but the storage levels in the two main reserviors are low.

"Although we have had some rains in August, September and October, the drought is not over," said Swietlik. "Yields per acre will decrease and the quality of fruit will be affected if there is no water. We hope that the rains will continue."

-TAMUK-
-Mary Daniel