Genetic mapping and utilization of quantitative trichome-mediated insect resistance in potato

Introgression of trichome-mediated insect resistance from the wild speciesSolanum berthaultii has become a major focus of the potato improvement program at Cornell University during the past twelve years. Several quantitative characters are involved in this resistance which is effective against a wide range of pest types. Correlative biochemical assays have been developed to assay specific components of the resistance, and the effects of the resistance on the target pests have been studied. Quantitative laboratory assays and specific measurements of insect behavior and biology have increased the precision of selection and enable the investigation of the genetic control of the resistance.We are currently using restriction fragment length polymorphisms (RFLPs) for genetic mapping of factors controlling the trichome traits fromS. berthaultii. Backcrosses to both the wild and the cultivated species parents have been evaluated for phenotypes contributing to the resistance mechanism, including trichome density, sucrose ester and polyphenol oxidase production by the trichomes, and the enzymatic browning reaction responsible for insect entrapment. Genetic maps are being developed for these progenies, using RFLP markers previously mapped in potato. Field and greenhouse trials under insect infestations are also being conducted with the mapping progeny. Our goal is to locate genes responsible for quantitative insect resistance by correlating RFLP variation at mapped loci with the trichome phenotypes and insect resistance. Genetic markers for these traits will be useful in transfer of the effective wild chromosomal segments into and among tetraploid potatoes, and for a better understanding of the resistance mechanism.     

New genes for disease resistances through somatic hybridization

Somatic hybridization, a process of combining protoplasts from different plants, can provide new sources of disease resistances for plants. In the case of wild and cultivatedSolanum species, the hybrids express resistances from each partner in the fusion and can often be crossed with cultivars to improve agronomic characteristics of the tubers. Restriction fragment length polymorphism (RFLP) analyses can provide a means for determining that the plants being investigated are actually hybrids as well as a means for following the introgression of DNA into progeny lines. These points are addressed in this paper with specific reference to somatic hybrids betweenSolanum brevidens and potato.     

Effective irrigation uniformity as related to root zone depth

Summary In models used for relating the yield to irrigation uniformity it has been assumed that the spatial distribution of irrigation water, as measured at the soil surface, is indeed the water distribution at any depth throughout the root zone. In the present paper the distribution of infiltrated water within the soil bulk, as determined by an analytic solution of the two-dimensional unsaturated flow equation, did not conform to this assumption. A new alternative definition of irrigation uniformity is proposed under the assumption that water uptake by roots does not affect the flux distribution within the soil profile. In this analysis the spatial distribution of irrigation water flux at the soil surface, which is the upper boundary condition of the flow equation, is assumed to be a sine function. The solution to this problem indicates that there is a damping effect, which increases with soil depth, on the surface flux fluctuations. Furthermore, the actual irrigation uniformity at a given depth below the soil surface depends upon the initial uniformity at the surface and the distance between adjacent water sources. The closer the water sources are to each other, the shallower is the depth needed to damp the oscillations down to a certain level. This may explain why the actual uniformity of drip irrigation is high while the detailed distribution is very nonuniform and on the other hand, why the actual uniformity of sprinkler guns is low while the detailed actual distribution is close to uniform. Two uniformity coefficients are derived in this study: 1. A depth dependent coefficient which is made up of the damping factor that multiplies the flux fluctuations at the soil surface; 2. An effective uniformity coefficient, which is an average of the depth dependent coefficient over a part or the entire root zone. Different degrees of uniformity are expected when water is applied by different irrigation systems having similar uniformity coefficients at the soil surface, but dissimilar distances between the emitters. Assuming that crop yield depends to some extent on the uniformity of water depth actually available to the roots, the yields associated with such irrigation systems will probably also vary.     

Nutritional stress in ficea sitchensis plantations in coastal British columbia: The effects of gaultheria shallon and declining site fertility

Examples of nutritional stress in conifer seedlings caused by competing ericaceous species (e.g. Calluna and Kalmia), have been reported in several parts of the world. Nutritional stress (primarily N deficiency) has been reported in Sitka spruce (Picea sitchensis) plantations growing in association with an ericaceous species, salal (Gaultheria shallon), in coastal British Columbia. Nutritional interference by salal was investigated on a chronosequence of sites up to 10 yr after clearcutting and slashburning. No direct evidence for an allelopathic contribution to the N stress was obtained. However, the rapid accumulation of salal fine roots and rhizomes, and the nutrients contained therein, provides a partial explanation for the observed stress symptoms. Soil analyses and seedling bioassays demonstrated a reduction in fertility in the period 8 to 10 yr after clearcutting and slashburning in comparison to the period 2 to 4 yr, which is believed to impose further nutritional stress on Sitka spruce. It is concluded that the nutritional stress in these Sitka spruce plantations is caused by a combination of (1) salal competition for nutrients and their subsequent immobilization in salal biomass, and (2) declining site fertility caused by the termination of the flush of nutrients (the assert period) that occurs in the immediate post-clearcutting and slashburning period. Sustaining good growth of plantations under such circumstances will require site nutrient management as well as vegetation management.     

Growth and erosion of thin solid films

Thin films that are grown by the process of sputtering are, by and large, quite unlike the smooth, featureless structures that one might expect. In general, these films have a complicated surface morphology and an extended network of grooves and voids in their interiors. Such features can have a profound effect on the physical properties of a thin film. The surface irregularities and the bulk defects are the result of a growth instability due to competitive shadowing, an effect that also plays a role in geological processes such as erosion. For amorphous thin films, the shadow instability can be described by a remarkably simple model, which can be shown to reproduce many important observed characteristics of thin film morphology.