Zane Smilowitz

Water deficit effects on potato leaf growth and transpiration: Utilizing fraction extractable soil water for comparison with other crops

Numerous studies have demonstrated that physiological responses of many crops to the fraction of extractable soil water conforms to a generalizable pattern. This suggests that differences among crops in their drought tolerance are largely due to differences in the total amount of transpirable water the crop can extract. Potato is frequently assumed to be more drought sensitive than other agronomic crops due, at least in part, to a shallow root system. In the research reported here, potato leaf growth and transpiration response to water deficits were determined as a function of fraction transpirable soil water (FTSW). Transpiration was unaffected by water stress until a critical FTSW was achieved when 64% to 80% of the extractable soil water was depleted depending on the cultivar. This was similar to the response reported for 8 other agronomic crops. In terms of transpiration, potato hypersensitivity to drought stress appears to be due to less effective soil water extraction. Leaf growth, however, showed a unique response to soil water deficits. Leaf growth began to decline when 40% of the extractable soil water was depleted. The associated critical FTSW was higher than any previously reported for all other crops. These data indicate that in addition to extracting less soil water, an additional physiological process related to leaf expansion must be contributing to the potato’s hypersensitivity to drought.CompendioNumerosos estudios han demostrado que las respuestas fisiológicas de muchos cultivos a la fracción extraíble de agua del suelo se comporta de una manera posible de generalizarse. Esto sugiere que las diferencias entre sus tolerancias a la sequía son debidas considerablemente a las diferencias en la cantidad total de agua de transpiración que el cultivo puede extraer. Se considera frecuentemente que la papa es más sensible a la sequía que otros cultivos debido, al menos en parte, a un sistema radicular superficial. En la investigación sobre la que aquí se informa, se determinaron las respuestas del crecimiento de las hojas y de la transpiración a los déficits de agua, como una función de la fracción transpirable del agua del suelo (FTSW). La transpiración no fue afectada por el estrés al agua hasta que era alcanzada una FTSW crítica, cuando se consumía del 64% al 80% del agua extraíble del suelo, dependiendo del cultivar. Esto fue similar a la respuesta reportada para otros ocho cultivos. En términos de transpiración, la hipersensibilidad de la papa al estrés a la sequía parece deberse a una extracción menos efectiva del agua del suelo. El crecimiento de las hojas, sin embargo, mostró una respuesta poco común a los déficits de agua en el suelo. El crecimiento de las hojas empezó a declinar cuando se consumió el 40% del agua extraíble del suelo. La FTSW crítica asociada fue mayor que en cualquier otro informe anterior sobre todos los otros cultivos. Esta información indica que además de extraer menos agua del suelo, un proceso fisiológico adicional relacionado a la expansión foliar debe estar contribuyendo a la hipersensibilidad de la papa a la sequía.

Spatial and Temporal Dynamics of Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Fields with Perimeter and Spatially Targeted Insecticides

Abstract Concern over insecticide resistance has led to the suggestion of spatially variable within-field management of Colorado potato beetle, Leptinotarsa decemlineata (Say). Here we compare L. decemlineata spatial and temporal dynamics, and potato yield, in fields treated with a narrow perimeter (5.5 m) of systemic imidacloprid supplemented with spatially targeted sprays to untreated fields and to fields where all rows received the systemic. The systemic targeted immigrating individuals which, having acquired the field through either flight or walking, first established themselves in the outer 5.5 m of the field. The perimeter treatment (≈25% of field area) reduced mean densities with no effect on timing of peak densities. Immigrating adults established similar spatial trends in both perimeter and untreated fields. Although trends in F1 larval densities have been shown to follow the patterns established by immigrating adults, trends in the F1 larval densities of the perimeter treatments diverged from adult patterns and developed highest densities in field centers. Immigrating adults had little to no spatial dependence in the covariance structure in any treatments. Spatial dependence in the covariance structure of F1 larval and F1 adult populations developed as density increased in both perimeter and untreated fields, with a tendency for increasing spatial dependence in perimeter fields, though this was not statistically significant. Comparing the perimeter to untreated fields, yields increased at a proportion that was higher than the proportion of land area treated, but remained significantly lower than the whole-field treatment. These results suggest that the perimeter tactic has promise as a site-specific resistance management program, but that refinement of border width is needed to optimize trade-offs among yield, quality, and long-term maintenance of susceptibility.

Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Prevention of host pupation at the endocrine level

Abstract RNA synthesis in normal Trichoplusia ni fifth instars and hosts parasitized at ca. 12 hr post-ecdysis was followed by measuring 3H-uridine incorporation with an autoradiographic technique. Uptake of 3H-uridine was high in control prothoracic glands at 6 and 30 hr and their cytology indicated an active secretory phase which was most pronounced at 30 hr. At the same time, glands of parasitized larvae decreased incorporation and appeared less active than controls. At > 75 hr, control fat body cells incorporated almost no label but were filled with RNA-protein granules apparently sequestered from the haemolymph preparatory to pupation. With respect to incorporation and cytology, fat body of parasitized larvae was unchanged from earlier in the instar, which indicates that the changeover to pupal preparations had not taken place. Imaginal wing disks incorporated label and grew appreciably in control larvae but abruptly decreased uptake and showed no size increase in parasitized larvae. Incorporation of Malpighian tubule, midgut epithelium, and certain muscles at > 75 hr showed little change in parasitized larvae, but in controls activity was reduced and histolysis occasionally was evident in muscles. The parasitoid, Hyposoter exiguae, apparently prevented host larvae from pupating by preventing activation of host prothoracic glands in the fifth instar. Other tissues which are normally activated for metamorphosis by the prothoracic glands continued normal larval activities until the end of the association.

Effect of trichome B exudate ofSolanum berthaultii Hawkes on consumption by the colorado potato beetle,Leptinotarsa decemlineata (Say)

The leaf extract fromS. berthaultii Hawkes (PI 473340) contains exudate from trichomes (type B). Consumption ofS. tuberosum var. Norchip foliage by the Colorado potato beetleLeptinotarsa decemlineata (Say) was reduced when treated with the leaf extract. The leaf extract from a resistantS. berthaultii clone without type B trichome had no antifeedant activity. It suggests that more than one mechanism of resistance to the Colorado potato beetle exists inS. berthaultii.

Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Parasitoid-induced histo- and cytopathology

Abstract The histology and cytology of Trichoplusia ni larvae were studied for evidence of abnormality or pathology induced by the solitary ichneumonid endoparasitoid, Hyposoter exiguae . Sample control and parasitized larvae were fixed every other day, and sections of these larvae were stained with mercuric-bromophenol blue. The fat body of parasitized larvae failed to show many of the changes characteristic of normally developing controls and, on the last day of parasitism, revealed extensive pathological changes. Spermatogenesis continued normally until the end of the association in parasitized hosts even though their development was halted in the fifth larval stadium. Parasitoid larvae seemed to secrete a proteinaceous material from their salivary and rectal glands into the host hemocoel. This material may be responsible for the pathological changes reported here. The parasitoids apparently fed on hemolymph alone until about 24 hr before emergence and pupation.

The vertical distribution of green peach aphids and its effect on a model quantifying the relationship between green peach aphids and a predator

The vertical distribution of green peach aphids (GPA) on potato plants was studied to estimate its impact on a model simulating the effects of a predator on GPA populations. This model is based on laboratory studies of a ladybird beetle feeding on GPA that was placed exclusively on the bottom leaf of a three leaf stem section. The model predicts the impact ofColeomegilla maculata (DeGeer) adults and third instar larvae on GPA populations over a range of temperatures and GPA densities.The vertical distribution of GPA in a potato field and the effects of different levels of aldicarb on this distribution were determined by counting all GPA on the upper, middle, and lower thirds of a stem in situ. A one leaf sub-sample was taken from each stem section as a comparison.The vertical distribution of GPA changed with aldicarb dose. Most GPA were found on the lower third of stems from plots treated with the lowest aldicarb doses. However, most GPA occurred on the upper third of the stems from plots treated with the highest aldicarb doses. This distribution changed midway through the season until most GPA occurred on the bottom third of the stems.C. maculata adults and third instar larvae preferentially search the upper and lower thirds of potato plants. This suggests thatC. maculata would be an effective early season predator, and that our model should over-predict the effect ofC. maculata on GPA populations late in the season.ResumenLa distribución vertical del áfido verde del duraznero (GPA) in plantas de papa fué estudiada para estimar su impacto en un modelo que simulaba los efectos de un predator sobre poblaciones del áfido verde. Este modelo está basado en estudios de laboratorio realizados con “mariquitas” alimentándose de áfidos verdes colocados únicamente sobre la hoja más inferior de una sección de tallo con 3 hojas. El modelo predice el impacto de adultos y larvas del tercer estadío deColeomegilla malucato (De Geer) sobre poblaciones del áfido a diferentes temperaturas y densidades.La distribución vertical del áfido verde en un campo de papa y el efecto de diferentes niveles de aldicarb fué determinado por contadas de todos los áfidos en los tercios superior, medio e inferior de un tallo “in situ”. Una hoja de cada tercio fué tomada como sub-muestra por comparación.La distribución vertical del áfido verde varió con la dosis de aldicarb. La mayoría de áfidos fueron encontrados in el tercio inferior de los tallos procedentes de parcelas tratadas con las dosis más bajas de aldicarb. Sin embargo, la mayoria de áfidos se encontraban en el tercio superior de los tallos procedentes de parcelas tratadas con las dosis más altas de aldicarb. Esta distribución empezó a cambiar a mediados de la campaña hasta que a la mayoria de áfidos se encontraban en el tercio inferior de los tallos.Adultos y larvas del tercer estadío deC. maculata prefieren los tercios superiores e inferiores de las plantas de papa. Esto sugiere queC. maculata podría ser un predator efectivo a los inicios del cultivo y que nuestro modelo podría sobre estimar el efecto deC. maculata en poblaciones del áfido verde en los períodos finales del cultivo.

Soluble protein electrophoretic patterns from two biotypes ofMyzus persicae (Sulzer), the green peach aphid

An SDS polyacrylamide disc gel electrophoretic study of the soluble hemolymph proteins from twoMyzus persicae (Sulzer) biotypes was conducted to determine if these biotypes could be distinguished from each other by their banding patterns. This study revealed that there were no differences between the two biotypes in terms of number and location of protein bands. Noticeable differences did occur between the biotypes in the intensity of specific bands. These differences could not be explained by proposed differences in the concentration of active enzymes regulating developmental rate in the biotypes.ResumenUn estudio electroprético en geles de polyacrilamida con SDS de las proteinas solubles de la hemolynfa, de dos biotipos deMyzus persicae (Sulzer) fué conducido para determinar si se podían diferenciar entre los dos biotipos por sus patrones de bandas. Este estudio reveló que no había ninguna diferencia entre los dos biotipos en cuanto al número y posición de las bandas protéicas.Se notaron diferencias entre biotipos en la intensidad de determinadas bandas. Estas diferencias no se pueden explicar con diferencias propuestas en la concentración de enzimas activas que regulan el desarrollo en los biotipos.