Dimethylnaphthalene and diisopropylnaphthalene for potato sprout control in storage: 1. Application methodology and efficacy

Dimethylnaphthalene (DMN) and diisopropylnaphthalene (DIPN) isomers applied as sprout suppressants to stored potatoes (cv. Russet Burbank) were evaluated for effects on sprout length and weight compared to chlorpropham (CIPC). One application of CIPC at 22 mg a.i. kg^-1 of tuber fresh weight (f.w.), and one or two applications of DMN and DIPN at 100, 200, and 300 mg a.i. kg^-1 f.w. were applied as thermal aerosol fogs. Two applications of DIPN at 300 mg a.i. kg^-1 f.w. were as effective as CIPC in suppressing sprout growth during ten months of storage. DMN also suppressed tuber sprout growth but was not as effective as two applications of DIPN or one application of CIPC. One application of DIPN or DMN at 300 mg a.i. kg^-1 f.w. was an effective suppressant of sprout growth on a short-term basis. Whole tuber residue analyses were also conducted. After ten months in storage, DMN and DIPN residue concentrations were equal to or less than those of CIPC.     

Comparative growth analysis of Russet Burbank potatoes at two Idaho locations

Detailed growth analyses were conducted with Russet Burbank potato to provide validation and parameterization data for a computer growth model being developed cooperatively at the University of Idaho and University of California, Davis. At each of two locations (Aberdeen and Kimberly, Idaho) plants were sampled seven times at about two-week intervals. Plants were separated into individual leaf blades, petioles, internodes, tubers, and roots. Leaf area indices and leaf elevation angles were determined in 20 cm strata. Plants at Kimberly emerged approximately 10 days prior to those at Aberdeen. At both locations, the increase in total dry weight was curvilinear for 30–40 days after emergence and then was linear until the end of the study. The maximum top weight per hill was slightly higher at Aberdeen, but near-maximum values occurred for much longer at Kimberly. Total leaf area at Aberdeen reached a maximum of approximately 4.0, while the maximum at Kimberly was 5.5. Root dry weight reached a maximum much earlier at Kimberly and the change in root dry weight paralleled that of tops in both places. Tuber initiation occurred approximately 19 June at both locations. Following an initial increase, tuber number/hill decreased for several weeks. Final tuber numbers per hill were approximately six at Aberdeen and 12 at Kimberly. Dry weight per tuber showed a curvilinear increase for 20–30 days and then was constant at 0.68 and 0.37 g/tuber.day at Aberdeen and Kimberly, respectively. Bulking rates were 17 and 21 g/m².day. Final yields were 39 T/ha at Aberdeen and 49 T/ha at Kimberly. The higher final tuber yield at Kimberly was the result of a higher rate of bulking and a longer leaf area duration.     

Sequence variation at a microsatellite locus (XGWM261) in hexaploid wheat (Triticum aestivum) varieties

The wheat microsatellite XGWM261 is of interest to wheat breeders because of its linkage to a commercially significant reduced height gene (Rht8). Previous studies have indicated that there are three major alleles at the XGWM261 locus and that the majority (90%) of varieties are homozygous, generating PCR products of 192,174, or 165 bp. As a preliminary investigation of heterozygosity and sequence variation at the XGWM261 locus in Australian wheat varieties, we cloned and sequenced PCR products from 24 hexaploid varieties of significance in Australian breeding programmes. Three major alleles of 192, 174 and 164 bp were found, but a165 bp allele was not detected. Prior genotyping via electrophoretic methods had indicated that 2 of the 24 (8%) varieties were heterozygous. Our results indicate that 6 varieties (25%) carry 2 or more of the major alleles. It is not clear whether this results from heterozygosity within individual seeds, or from heterogeneity of breeding stocks. With respect to the microsatellite region itself, we found that the 174 bp and 164 bp alleles actually represent (CT)₁₁AG and (CT)₆AG motifs (respectively) rather than(CT)₁₂ and (CT)₇. This finding has diagnostic potential. A further 2 varieties also carry an interrupted (CT)_nCC(CT)_n microsatellite not previously recorded. It is unclear whether this represents a separate allelic lineage or is simply the result of replication error. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation in resistance of Mexican landraces of maize to maize weevil Sitophilus zeamais,in relation to taxonomic and biochemical parameters

Summary Accessions representing twenty eight landraces of maize were assessed for susceptibility to the maize weevil, Sitophilus zeamais in standardized resistance tests. Susceptibility parameters such as weight loss of grain, number of insect progeny produced, the Dobie index of susceptibility, and oviposition on grain were found to vary significantly by genotype, with exceptional resistance found in accessions representing the Naltel, Chapalote and Palomero landraces. As in improved genotypes, susceptibility was negatively correlated to phenolic and protein content of the variety tested but positively correlated to moisture content. A detailed analysis of the phenolics revealed the presence of diferulate which may contribute to mechanical resistance of the seed by cross-linking of cell wall hemicelluloses. A canonical discriminant analysis of the resistance data suggests that most of the five landrace groupings are significantly different. The ancient indigenous and prehistoric mestisos groupings are sources of resistant genotypes.     

CIPC residues on stored Russet Burbank potatoes: 1. Maximum label application

Residue concentrations of chlorpropham (CIPC) on stored Russet Burbank potatoes were evaluated after thermal aerosol treatment at maximum labeled rates. The aerosol was applied after the potatoes had been placed in the storage structure and the wound healing process was complete. Average residue concentrations four days after the initial application ranged from 6 to 8 mg/kg fresh tuber weight depending on the storage temperature and the application rates. A second aerosol treatment applied 90 days after the first treatment kept the residue concentrations above 5 mg/kg for the duration of the storage period. A direct spray application to the tubers at various times during the study raised the average CIPC concentration an additional 2 to 3 mg/kg. All CIPC residue concentrations measured on tubers in this study were below the EPA established (1996) tolerance of 30 mg/kg. Residue concentrations of CIPC were greater on potatoes near the bottom of the pile than near the top of the pile. These variations in CIPC residue concentrations (3–8 mg/kg between top and bottom of the bulk pile) are appropriate justification for the development of improved application methodology.     

Efficacy of chlorine dioxide for disease control on stored potatoes

The post-harvest application of chlorine dioxide (ClO₂) was evaluated as a disease suppressant for stored potatoes. Chlorine dioxide was prepared by acidifying a buffered sodium chlorite solution with a food grade acid.In vitro studies verified the effectiveness of C1O₂ at low concentrations (ED₅₀ = 2 to 122 ppm) againstErwinia carotovora (soft rot),Fusarium spp. (dry rot) andHelminthosporium solani (silver scurf). Evaluations of tubers inoculated withPhytophthora infestans (late blight) andFusarium spp. or infected withH. solani and then treated with ClO₂ either going into storage or through the humidification system resulted in a lack of disease suppression. Inconsistent performance of C1O₂ in storage appeared to be a result of several contributing factors. Chlorine dioxide concentrations varied greatly (up to six-fold), depending upon the method of activating and diluting sodium chlorite solutions. Chlorine dioxide is a gas soluble in water and, therefore, is easily released from solution (25% –75% loss) into the air when applied as an aqueous spray. Chlorine dioxide reacts quickly with the tuber and associated organic matter, thereby reducing the effectiveness. Applying higher than currently registered rates may be necessary to achieve measurable disease suppression.     

The impact of seasonal variability in wildlife populations on the predicted spread of foot and mouth disease

Modeling potential disease spread in wildlife populations is important for predicting, responding to and recovering from a foreign animal disease incursion such as foot and mouth disease (FMD). We conducted a series of simulation experiments to determine how seasonal estimates of the spatial distribution of white-tailed deer impact the predicted magnitude and distribution of potential FMD outbreaks. Outbreaks were simulated in a study area comprising two distinct ecoregions in South Texas, USA, using a susceptible-latent-infectious-resistant geographic automata model (Sirca). Seasonal deer distributions were estimated by spatial autoregressive lag models and the normalized difference vegetation index. Significant (P < 0.0001) differences in both the median predicted number of deer infected and number of herds infected were found both between seasons and between ecoregions. Larger outbreaks occurred in winter within the higher deer-density ecoregion, whereas larger outbreaks occurred in summer and fall within the lower deer-density ecoregion. Results of this simulation study suggest that the outcome of an FMD incursion in a population of wildlife would depend on the density of the population infected and when during the year the incursion occurs. It is likely that such effects would be seen for FMD incursions in other regions and countries, and for other diseases, in cases in which a potential wildlife reservoir exists. Study findings indicate that the design of a mitigation strategy needs to take into account population and seasonal characteristics.