Multispectral aerial and satellite remote sensing plays a major role in crop yield prediction due to its ability to detect crop growth conditions on spatial and temporal scales in a cost effective manner. Many empirical relationships have been established in the past between spectral vegetation indices and leaf area index, fractional ground cover, and crop growth rates for different crops through ground sampling. Remote sensing-based vegetation index (VI) yield models using airborne and satellite data have been developed only for grain crops like barley, corn, wheat, and sorghum. So it becomes important to validate and extend the VI-based model for tuber crops like potato, taking into account the most significant parameters that affect the final crop yield of these crops.

In the past 10 years we have witnessed the beginnings of the study of soil ecology as a unified science, and the general realization by soil scientists, farmers, and land managers that many of the most important economic aspects of soil health are controlled by biological factors. This research focuses on alterations in a tropical soil microarthropod community under differing intensive agricultural protocols: native vegetation, pastures and cropland, during June, July and August 1998. The effect of pesticides in potato cultivation was also studied. In the Ecuadorean montane forest, 361 morphospecies of soil arthropods, were classified during the three sampling months. August was the month with highest abundance and diversity. Acari, Coleoptera, Collembola, Diptera and Homoptera were the most abundant orders present in all the three types of land management. The native vegetation had the most abundant and diverse representation of all soil arthropod taxa compared to the pastures and croplands. Coleoptera, Diptera, Diplopoda, Diplura and Hemiptera were significantly more diverse in native vegetation than in pastures and croplands. The most abundant functional groups were the fungivores, herbivores and predators. The abundance of functional groups was significantly higher in the native vegetation for predators, herbivores and detritivores. 115 morphospecies of soil arthropods were identified in the study of arthropod response to pesticides in a complete randomized potato plot. Seasonal effects were documented for Acari, Collembola, Diptera, and Homoptera. Predators were most abundant in July and fungivores decreased in September. Neither arthropod orders nor functional groups showed a significant change in abundance between different treatments. Only Homoptera showed an increase in its abundance in the third sampling date and only in the Antracol plots. The potato plants in the whole block showed poor productivity, suggesting that the whole system was stressed by the fungal pest. / Graduation date: 2000

Thesis (Ph. D.)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

Thesis (M.Sc.)(Plant Biotechnology))--University of Pretoria, 2002. / Summaries in Afrikaans and English. Includes bibliographical references.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Corinne Valdivia. Includes bibliographical references.

No description available.

Many parasitic diseases display symptoms beyond the areas invaded by the parasite itself. This suggests that toxic metabolic products of the pathogen diffusing in front of its advancing growth brings about derangements in unoccupied tissues at times far remote from the focus of infection. [...]

Salinity problems seriously affect agricultural production by reducing crop yield and arable land. The evaluation of potato genotypes (Solanum spp.) for their salinity (NaCl) tolerance in conventional field trials is time consuming and labour intensive. The results are often confounded by many field and environmental variations. In vitro bioassays can overcome some of these difficulties by providing faster, more convenient and dependable methods for screening and selection of salt tolerant potato genotypes. The objective of this research was to develop in vitro bioassay methods for screening and selection of salt tolerant potato. Under in vitro NaCl stress conditions, seed germination, early seedling growth, and single-node cutting bioassays were used to evaluate salinity tolerance. The selected genotypes were further tested with three in vitro bioassays (single-node cuttings, root tip segments, and microtuberization). The rankings of potato cultivar salinity tolerance were similar in these bioassays. The single-node cutting bioassay was recommended because it was simpler to perform than the root tip segment and microtuberization bioassays and did not exclude certain genotypes as did the microtuberization bioassay. The in vitro bioassay rankings were compared with yield ranking in field lysimeters. In both the in vitro and in vivo saline stress experiments, cvs. Kennebec and Russet Burbank were more salt tolerant than Norland. The tubers and microtubers harvested from previous experiments were tested in the greenhouse to investigate salinity carry-over effect for seed tuber production. There was no apparent residual carry-over effect found. Microtuber yield increase in the presence of low NaCl concentration was induced primarily by specific ion (Na+), and not osmotic effects. This research clearly indicated that in vitro bioassays are relatively simple, rapid, convenient, repeatable, and agree with the field lysimeter results. They can be used to substitute for f

Tubers of Russet Burbank were surface disinfested and 3 mm diameter by 3 mm deep wounds were made with cork borer. The holes were inoculated with 20muL of 104 macroconidia/ml suspension of (Fusarium sambucinum) or 20muL of 104 sporangia/ml suspension (Pythium ultimum) and incubated under mist. For infection studies, the inoculated tubers were exposed to 0--48 h of mist at 4--20ºC, dried and stored at 16ºC and 95% RH in growth chamber with forced air for 15 d (F. sambucinum), whereas stored at 12ºC and 95% RH for 30 d (P. ultimum). For lesion expansion studies tubers exposed to 24 h wet at 16ºC were stored in growth chambers at 4, 8, 12, and 16ºC for 15--90 d. At the end of storage tubers were cut and the volume of diseased area was measured. Models explained 94.2% of the variation in infection and 99.7% in lesion expansion for F. sambucinum . Whereas, models explained 96.7% of the variation in infection and 99.6% lesion expansion for P. ultimum. (Abstract shortened by UMI.)

Potato requires high levels of nitrogen fertilizer. Up to now in Quebec, no nitrogen fertilizer recommendation has been based on nitrogen availability in the soil, even those soil nitrogen testing is available. The objectives of this study were: (1) to determine the relation between soil nitrate-N content, nitrogen fertilization and potato yield; and (2) to determine the time and the sampling depth of soil most appropriate to predict potato yields and response to nitrogen fertilizer under Quebec conditions. Soil samples were taken at two depths at planting and at hilling time in 28 sites fertilized at four levels of nitrogen. Laboratory measures of nitrate-N were carried out on those samples. A combination of nitrate-N and nitrogen fertilisation gave the best explanation of the variation potato yields. A maximum of 46% of yield variation was attributed to the combination of those two factors in general. Best coefficients of determination were obtained when the sampling of nitrate-N was done at planting time compared to time. Regression models predicted nitrogen fertilizer needs of 89 to 200 kg ha$ sp{-1}.$ The same conclusions were found in the case of the variety Superior alone. The variation of yield explained was up to 62%. Regression models predicted nitrogen fertilizer needs of 77 to 224 kg ha$ sp{-1}$ for Superior. It was concluded that the analysis of soil nitrate-N can improve the prediction of nitrogen fertilizer needs for an optimum potato production.