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November-December 2002

Cover: With a production value of $138 million in 2001, rice is an important California field crop. Grown in flooded conditions, rice is also one of the crops considered most sensitive to salinity. In a series of field and greenhouse studies, scientists with UC and USDA determined that rice is significantly more sensitive to salinity than previous guidelines suggest. By carefully managing water in fields, particularly at growth stages when rice is most salt-sensitive, farmers can limit crop damage and optimize yields. Aove, Former UC Davis post-graduate researcher Bill Thomas takes measurements in a grower's rice field, whcich was outfitted with large metal rings to study the impacts of various salinity levels in soil and water. Photo by Jack Kelly Clark .

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California Agriculture, November-December 2002

Volume 56, Number 6
Saline water and rice yields - a delicate balance

Peer-reviewed Research Articles

Water management practices can affect salinity in rice fields
by Steven C. Scardaci, Michael C. Shannon, Stephen R. Grattan, Austine U. Eke, Stacey R. Roberts, S. Goldman-Smith, James E. Hill
pp184-188, doi#10.3733/ca.v056n06p184
Abstract
Water management practices in California rice production can affect salinity in the field. This is particularly important because rice is one of the most sensitive crops to salinity. We extensively monitored salinity patterns in dozens of rice fields in Colusa and Glenn counties, in order to determine how salinity varies from basin to basin and to compare salinity patterns under different irrigation systems. We found that the fields most vulnerable to salinity damage were those with higher soil salinity and using irrigation water sources initially high in salinity, particularly nondistrict sources that are combinations of well and drain water. Long water holding periods, while effective in reducing pesticide concentrations in rice fields, can contribute to salinity increases in bottom basins. Salinity can increase with either conventional or static irrigation management systems, but the salinity pattern in the field will be different.
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Rice is more sensitive to salinity than previously thought
by Stephen R. Grattan, Linghe Zeng, Michael C. Shannon, Stacy R. Roberts
pp189-198, doi#10.3733/ca.v056n06p189
Abstract
Field studies conducted by UC and under controlled greenhouse conditions by the U.S. Department of Agriculture's Agricultural Research Service indicate that rice is more sensitive to salinity than current guidelines suggest. This information is particularly important to rice growers who have experienced salinity problems after holding water on fields for longer time periods to reduce pesticide loading into the Sacramento River. Our field experiments show that an average seasonal salinity of the field water in excess of 1.9 deciSiemens per meter (dS/m) can reduce grain yields; current guidelines indicate that salinity affects rice yield at or above 3.0 dS/m. Salinity had a negative impact on a number of yield components including stand establishment; panicles, tillers and spikelets per plant; floret sterility; individual grain size; and even delayed heading. The emergence and early seedling growth stages were most sensitive to salinity, as was the three-leaf to panicle-initiation stages. Irrigation management practices should be adopted to minimize salinity during these critical growth stages.
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California mealybugs can spread grapevine leafroll disease
by Deborah A. Golino, Susan T. Sim, Raymond Gill, Adib Rowhani
pp196-201, doi#10.3733/ca.v056n06p196
Abstract
UC Davis's Foundation Plant Materials Service (FPMS) maintains the disease-tested, professionally identified collection of grape scion and rootstock varieties, which is the core of the California Grapevine Registration and Certification Program. In 1992; newly developed serological testing techniques revealed the presence of grapevine leafroll-associated viruses (GLRaVs) in previously healthy vines in an older foundation propagating block, indicating active and recent virus spread. FPMS responded by increasing isolation distances and implementing a comprehensive virus screening program using the new methodology. The critical problem was the lack of information on leafroll virus epidemiology. When the distribution of infected plants in the old vineyard was mapped, new infections were frequently adjacent to known diseased grapevines. This study examined the ability of mealybugs, a putative leafroll vector, to transmit this group of viruses. We were able to confirm that four species found in California — obscure, longtailed, citrus and grape mealybug — can transmit GLRaV-3 isolates. This is the first experimental evidence of grapevine leafroll virus transmission by obscure and grape mealybug. In addition, we report for the first time that GLRaV-5 can be transmitted by longtailed mealybug.
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Proper harvest timing can improve returns for intermountain alfalfa
by Steve B. Orloff, Daniel H. Putnam, Steve C. Blank
pp202-208, doi#10.3733/ca.v056n06p202
Abstract
Harvest timing has a profound effect on the yield and forage quality of alfalfa hay. Early harvest results in low yield but high forage quality and price, while delayed harvest increases yield but reduces forage quality and price. Since gross revenue is a function of both yield and price, it is important for growers to select the optimum cutting schedule. We quantified a biological relationship among yield, forage quality and day of harvest, using the results from 2 years of field studies at locations in the intermountain alfalfa production region of California. An economic analysis, including a decision model, was developed to enable producers to assess current market conditions and seasonal effects, and in turn select the most profitable harvest timing. Our analysis demonstrated that no single harvest strategy is always best. The most profitable approach depends on the rate of change in yield and quality for that season and the current price differential between the quality market classes for alfalfa hay.
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Editorial, News, Letters and Science briefs

EDITORIAL: Research budget cuts challenge ANR
by W.R. Gomes
pp178, doi#10.3733/ca.v056n06p178
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The buzz on mosquito, malaria genetic codes
Editors
pp180, doi#10.3733/ca.v056n06p180a
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Centers to combat “agro-terror”
Editors
pp180-181, doi#10.3733/ca.v056n06p180b
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State budget calls for 10% research cut
Editors
pp181, doi#10.3733/ca.v056n06p181a
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UC offers online course for grape pest advisors
Editors
pp181, doi#10.3733/ca.v056n06p181b
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SOD pathogen hits coast redwoods, Douglas fir
by Janet White
pp182, doi#10.3733/ca.v056n06p182
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Beahrs international program trains professionals in sustainable development
by Janet Byron
pp183, doi#10.3733/ca.v056n06p183
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Premating and Postmating Isolation among Populations of Metaseiulus occidentalis (Nesbitt) (Acarina: Phytoseiidae)

by Marjorie A. Hoy, Frances E. Cave
pp1-20, doi#10.3733/hilg.v56n06p020
Abstract
Differences in premating behavior patterns and timing, both within and between populations, were observed among reciprocal crosses of five populations of the western predatory mite, Metaseiulus occidentalis (Nesbitt). One population that was subjected to three selections for enhanced premating isolation showed no selection response. Postmating isolation in five of the eight pairs of reciprocal crosses of M. occidentalis colonies resulted in the deposition of shriveled eggs and reduced numbers of apparently normal eggs. Reciprocal crosses usually exhibited different degrees of incompatibility; no apparent pattern with regard to geographic origin of the colonies was found in the degree of postmating isolation. The potential impact of postmating isolation on population dynamics was evaluated in reciprocal crosses of two populations using life table techniques. One colony was a strain that had been artificially selected in the laboratory for resistance to permethrin (Immature Selection-38), the other a population collected from a California pear orchard (McCall Pears). In the Immature Selection female (IS) X McCall Pear (MP) male cross, IS females produced fewer eggs than MP females in the reciprocal cross. Of the eggs deposited by the IS females mated to MP males, substantially more eggs shriveled than in the reciprocal cross. In addition, most of the surviving F1 progeny in the IS female X MP male cross were males. The net reproductive rate (Ro) of the MP female X IS male cross was 10.58, but only 0.92 for the reciprocal cross. The intrinsic rate of increase (rm) of the MP female X IS male cross was 0.213 and zero for the reciprocal cross. The wide geographic distribution of M. occidentalis throughout western North America enhances the likelihood that genetically distinct populations have developed. The data presented here and other data previously obtained on dispersal rates, discreteness of pesticide-resistant populations, and differences in diapause attributes of geographic strains indicate that M. occidentalis is subdivided into distinct populations, some of which are partially reproductively isolated from others through postmating isolating mechanisms. No clear pattern has emerged, however, that would allow us to predict which populations are completely compatible. Populations that are geographically distant may show little reproductive isolation, while others that are adjacent may be partially reproductively isolated, and differences may occur between reciprocal crosses. In the case of the permethrin-resistant strain (IS), the degree of reproductive isolation after release into orchards or vineyards that contain native M. occidentalis cannot be predicted. It would be desirable to have such reproductive isolation, because permethrin resistance is polygenically determined in this colony and outcrossing can result in loss of resistance. Thus, IS (permethrin-resistant) populations released into North American orchards or vineyards will have to be maintained as pure populations through selection with permethrin rather than through reproductive incompatibility because of our inability to predict whether postmating isolation will occur.
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Premating and Postmating Isolation among Populations of Metaseiulus occidentalis (Nesbitt) (Acarina: Phytoseiidae)

by Marjorie A. Hoy, Frances E. Cave
pp1-20, doi#10.3733/hilg.v56n06p020
Abstract
Differences in premating behavior patterns and timing, both within and between populations, were observed among reciprocal crosses of five populations of the western predatory mite, Metaseiulus occidentalis (Nesbitt). One population that was subjected to three selections for enhanced premating isolation showed no selection response. Postmating isolation in five of the eight pairs of reciprocal crosses of M. occidentalis colonies resulted in the deposition of shriveled eggs and reduced numbers of apparently normal eggs. Reciprocal crosses usually exhibited different degrees of incompatibility; no apparent pattern with regard to geographic origin of the colonies was found in the degree of postmating isolation. The potential impact of postmating isolation on population dynamics was evaluated in reciprocal crosses of two populations using life table techniques. One colony was a strain that had been artificially selected in the laboratory for resistance to permethrin (Immature Selection-38), the other a population collected from a California pear orchard (McCall Pears). In the Immature Selection female (IS) X McCall Pear (MP) male cross, IS females produced fewer eggs than MP females in the reciprocal cross. Of the eggs deposited by the IS females mated to MP males, substantially more eggs shriveled than in the reciprocal cross. In addition, most of the surviving F1 progeny in the IS female X MP male cross were males. The net reproductive rate (Ro) of the MP female X IS male cross was 10.58, but only 0.92 for the reciprocal cross. The intrinsic rate of increase (rm) of the MP female X IS male cross was 0.213 and zero for the reciprocal cross. The wide geographic distribution of M. occidentalis throughout western North America enhances the likelihood that genetically distinct populations have developed. The data presented here and other data previously obtained on dispersal rates, discreteness of pesticide-resistant populations, and differences in diapause attributes of geographic strains indicate that M. occidentalis is subdivided into distinct populations, some of which are partially reproductively isolated from others through postmating isolating mechanisms. No clear pattern has emerged, however, that would allow us to predict which populations are completely compatible. Populations that are geographically distant may show little reproductive isolation, while others that are adjacent may be partially reproductively isolated, and differences may occur between reciprocal crosses. In the case of the permethrin-resistant strain (IS), the degree of reproductive isolation after release into orchards or vineyards that contain native M. occidentalis cannot be predicted. It would be desirable to have such reproductive isolation, because permethrin resistance is polygenically determined in this colony and outcrossing can result in loss of resistance. Thus, IS (permethrin-resistant) populations released into North American orchards or vineyards will have to be maintained as pure populations through selection with permethrin rather than through reproductive incompatibility because of our inability to predict whether postmating isolation will occur.
PDF