Screening for drought tolerance and genetic diversity of wheat varieties using agronomic and molecular markers.

BACKGROUND: The future predictions for frequent and severe droughts will represent a significant threat to wheat yield and food security. In this context, breeding has proven to be the most efficient approach to enhance wheat productivity in dry environments. METHODS AND RESULTS: In this study, both agronomic and molecular-based approaches were used to evaluate the response of twenty-eight Tunisian wheat varieties to drought stress. The primary objective was to screen these varieties for drought tolerance using molecular and agro-morphological markers. All varieties were significantly affected by drought stress regarding various traits including total dry matter, straw length, flag leaf area, number of senescent leaves, SPAD value, grain yield and grain number. Furthermore, substantial variability in drought-stress tolerance was observed among wheat genotypes. The cluster analysis and principal component analyses confirmed the existence of genotypic variation in growth and yield impairments induced by drought. The stress susceptibility index (SSI) and tolerance index (TOL) proved to be the most effective indices and were strongly correlated with the varying levels of genotypic tolerance. The genotyping evaluation resulted in the amplification of 101 alleles using highly polymorphic 12 SSR markers, showed an average polymorphism of 74%. CONCLUSIONS: Taken together, the combination of agronomic and molecular approaches revealed that Karim, Td7, D117 and Utique are the most drought-tolerant wheat varieties. These varieties are particularly promising candidates for genetic improvements and can be utilized as potential genitors for future breeding programs in arid and semi-arid regions.

Molecular Detection of Strain L47 of Aureobasidium pullulans, a Biocontrol Agent of Postharvest Diseases.

The strain L47 of Aureobasidium pullulans is an effective biocontrol agent of postharvest diseases. When applied in the field before harvesting it requires a specific monitoring method to evaluate colonization and dispersal in the environment. The randomly amplified polymorphic DNA technique (RAPD) was used for a preliminary screening of A. pullulans genetic variability among 205 isolates. This approach allowed the selection of a 1.3-kb fragment (L4) present solely in isolates L47 and 633. In Southern blots, a digoxigenin (DIG)-labeled L4 amplicon specifically recognized the corresponding fragment present in the polymorphic pattern of L47 and 633. The L4 fragment was cloned, sequenced, and used to design two sequence-characterized amplification region (SCAR) primers and a 242-bp riboprobe. Both the SCAR primers and the 242-bp DIG-labeled riboprobe were highly specific for L47. In classical polymerase chain reaction (PCR), with a series of 10-fold dilutions of L47 DNA, the limit of detection was 20 pg/µl. The Ap13 primer was also modified to obtain a Scorpion primer for detecting a 150-bp amplicon by fluorescence emitted from a fluorophore through a self-probing PCR assay. This assay specifically recognized the target sequence of L47 strain over a number of other A. pullulans isolates in field-treated grape berry washings. The limit of detection was 105 cells per ml, i.e. 10 times higher than the limit of the CFU method. The method is also proposed as a way to demonstrate the ability of L47 strain to penetrate the epidermis of sweet cherry fruits and to track it in the mesocarp.