Inheritance of race 1.2 Fusarium wilt resistance in four melon cultivars

The resistance to Fusarium oxysporum f.sp. melonis (Fom) race 1.2 has been studied in melons, such as the Portuguese accession ‘BG-5384’ and in the Japanese ‘Shiro Uri Okayama’, ‘Kogane Nashi Makuwa’, and ‘C-211’, since a good characterization of the resistance is necessary before its introgression into commercial varieties. These four melon accessions showed a high level of resistance to races 0, 1, and 2 of Fom, indicating that the partial resistance to the race 1.2 previously detected may not have been race specific. To determine the mode of inheritance of the resistance to Fom race 1.2, the F₁, F₂, BCP_R, and BCP_S generations from the crosses between the four resistant accessions above and ‘Piel de Sapo’, a Fom race 1.2 susceptible melon, were developed. They were subsequently inoculated with two Fom isolates, one from the pathotype 1.2Y and the other from the pathotype 1.2W. The area under the disease progress curve was determined for each inoculated plant, and the data were analyzed. We show that the resistance seen in these accessions is polygenically inherited with a complex genetic control because many epistatic interactions were detected. The three epistatic effects; additivity × additivity, dominance × dominance, and dominance × additivity are present and significant, with differing magnitudes from one cross to the next. The relatively low heritabilities, and these epistatic effects make difficult the improvement of the resistance, from these sources, through a standard selection procedure.     

Genetic polymorphism of plastid DNA in Tunisian date-palm germplasm (Phoenix dactylifera L.) detected with PCR-RFLP

Fifteen plastid fragments were amplified from a set of Tunisian date-palm accessions by PCR with consensus primers and analysed by RFLP. Polymorphic DNA bands were obtained as reliable molecular markers to estimate genetic distances among the accessions and to examine their phylogenetic relationships. The ctDNA PCR-RFLP method permitted the identification of two haplotypes that differ in the presence or absence of the HinfI restriction site. Phenetic groups composed of cultivars clustered together but does not constitute monophyletic groups. This typology agrees with the haplotypes' organization and provides a common genetic background within the implied varieties.     

Nitrate contents in some vegetables in Tunisia

This study reports the nitrate level of 22 vegetables species collected from 40 farms in several locations of an intensive agricultural area in two regions of Tunisia (Sousse and Monastir). Nitrate levels ranged between 57 and 2970 mg kg^?1. The highest and the lowest levels were found in turnip and tomato, respectively. Only five species (potato, field bean, cauliflower, pea and artichoke) had exceeded the norms established by the World Health Organization. Factors influencing nitrate accumulation in some vegetables were analyzed and discussed. It was observed that nitrate contents in vegetables varied depending on the type of vegetables, genetic factor, level of nitrogen fertilization and soil nitrogen content.     

Weed flora and seed yield in quinoa crop (Chenopodium quinoa Willd.) as affected by tillage systems and fertilization practices

The effects of tillage system and fertilization regimes on weed flora in quinoa (Chenopodium quinoa Willd.) were evaluated by means of two field experiments in 2011 and 2012. The experiments were laid out in a split-plot design with two main plots (conventional and minimum tillage) and four sub-plots (fertilization regimes). The results indicated that weed biomass and density in quinoa were influenced by the different fertilization and tillage treatments. Moreover, seed yield in conventional was 5%–13% higher than that of minimum tillage, probably due to the lower weed density and biomass. Concerning fertilization treatments, total weed density and biomass increased under manure application and inorganic fertilization. Tillage effects on weeds were species specific. The density of perennial weeds such as purple nutsedge (Cyperus rotundus L.) and the density of small-seeded weeds such as redroot pigweed (Amaranthus retroflexus L.) and common purslane (Portulaca oleracea L.) were significantly lower under the conventional tillage than under the minimum tillage system.     

Physiological races of Fusarium oxysporum f.sp. melonis in Tunisia

Fusarium wilt of melon, caused by Fusarium oxysporum f.sp. melonis (Fom), is an important disease; races of the pathogen were identified by inoculating differential standard host cultivars. A total of ten isolates that were obtained from 23 fields located in four different geographical regions were identified as pathogenic. Results indicate that all four known Fom races, namely, 0, 1, 2 and 1.2, were found in north and middle Tunisia. Race 1.2 was the most prevalent.     

Pirimiphos-methyl and benalaxyl losses in surface runoff from plots cultivated with potatoes

Abstract: Losses of pirimiphos-methyl and benalaxyl in runoff water from clay soil plots cultivated with potatoes and of differing soil surface slopes were determined over approximately 120 days (1 October 1999-28 January 2000). The plot slopes were 0, 1, 2.5 and 5%, and soil erosion increased with the slope from 610 to 1760kgha(-1). The runoff of surface water was between 3.1 and 16.6% of the rainfall. Surface runoff was highest for the fifth and seventh runoff events due to rainfall, 51 days and 72 days after the first pesticide application. The maximum concentrations of the two pesticides in runoff occurred in the plots with the greatest slope (5%) during the fifth runoff event, November 21, 1999 reaching 8.4 and 12.3 microg litre(-1) for pirimiphos-methyl and 17.8 and 20.2 microg litre(-1) for benalaxyl in tilled and untilled plots respectively. The cumulative losses of pirimiphos-methyl in surface runoff from tilled and untilled plots with a slope 5% were estimated at only 0.37 and 0.59% of the initial applied active ingredient, respectively, while for plots with a slope 0% the percentages were 0.013 and 0.018%. For benalaxyl the corresponding values from tilled and untilled plots were 1.69 and 1.76% (slope 5%), and 0.062 and 0.085 (slope 0%). Degradation of the pesticides in the topsoil was monitored from October 1999 and May 2000. Cultivation of potatoes decreased the half-life of the two pesticides compared to the untilled fields, for pirimiphos-methyl from 16.7 to 9.2 days and for benalaxyl from 26.7 to 12.6 days. The slope of soil surface and the different sorption capacities for the compounds are the main parameters which influenced the transportation of studied pesticides, pirimiphos-methyl and benalaxyl residues via surface water in soil-water systems.     

INFLUENCE OF DIFFERENT SEED PRIMING METHODS FOR IMPROVING SALT STRESS TOLERANCE IN LETTUCE PLANTS

Seeds of lettuce, variety Romaine were subjected to different priming treatments such as water, potassium nitrate (KNO₃) and gibberellic acid (GA₃). Seedlings obtained from primed (Pr) and nonprimed (NP) seeds were grown in a hydroponic culture system supplemented with 0, 100 or 200 mM sodium chloride (NaCl). The different physiological and biochemical responses were studied 15 days after treatment. Under NaCl, the dry weight was higher in plants derived from hydro-primed (HP) seeds when compared to NP, osmoprimed (KNO₃P), and hormonal primed (GA₃P) ones. Under control and 100 mM NaCl treatment, malondialdehyde (MDA) content and EL did not show any correlation with activities of gaiacol peroxidase (GPX) and catalase (CAT), but did with the increase in reduced ascorbate (AsA) and total ascorbate contents. The results indicated that plants derived from HP seeds exhibited higher adaptive potential under salinity stress. Our findings suggest that a hydropriming technique can be used as a simple commercial approach to alleviate the effects of NaCl induced stress in lettuce plants.     

Effect of genotype and growing season on nitrate accumulation and expression patterns of nitrate transporter genes in potato (Solanum tuberosum L.)

Nitrate (NO₃^?) is the most important source of mineral nitrogen (N) affecting the vegetative growth, the tuber yield and the quality of potato (Solanum tuberosum L.). The screening of 16 potato cultivars for low nitrate content was reported and the effects of genotype and experimental factors on nitrate accumulation were studied. Both genotype and growing season had a highly significant effect on dry weight, number of tubers/plant, yield and nitrate accumulation in potato which varied significantly from one genotype to another. Furthermore, nitrate accumulation varies with the season, being higher in the first season (autumn) than in the second season (spring), for all the genotypes. The cultivars Safrane and Universa followed by Actrice and Alaska produced the highest tuber yield/plant during the first and second season, respectively, accumulating higher quantities of nitrate compared to other cultivars. Ponomera cultivar was of interest from a breeding perspective due to both combining best tuber yield/plant and low nitrate accumulation for both growing season. Expression pattern of nitrate transporter genes (StNRT1.2, StNRT1.5 and StNRT2.1) has been reported. Thus, these genes were differentially expressed which could be explained in part by the difference in nitrate accumulation rate between the studied cultivars. The results showed that high accumulator genotype got significant higher expression level of StNRT1.2, StNRT1.5 or StNRT2.1 which lead to the higher nitrate uptake rate and consequently higher nitrate accumulation than low accumulator genotype.