Improving Peach Fruit Quality Traits Using Deficit Irrigation Strategies in Southern Tunisia Arid Area.

The peach (Prunus persica L.) is one of Tunisia's major commercial fruit crops and is considered one of the biggest water consumers of all crops. In warm and arid areas of southern Tunisia, irrigation is necessary to ensure orchard longevity and high yield and fruit quality. Nevertheless, under water-scarcity conditions and low water quality, water management should rely on efficient deficit irrigation strategies. In this study, sustained deficit irrigation (DI) and partial root-zone drying (PRD50) at 50% of crop evapotranspiration (ETc) were evaluated for their impact on the primary and secondary metabolites of the peach fruit of early cultivar Flordastar grown in the Tataouine region. A full irrigation (FI) treatment at 100%, etc., was used as a control treatment. Color, dry-matter content, firmness, organic acids, sugars, phenolic compounds, vitamin C, ß-carotene and minerals were assessed on harvested mature fruits. Dry-matter content and firmness increased significantly under DI and PRD50 (13% and 15.5%). DI fruit had the highest soluble-solid content (SSC), reaching Brix values of 14.3°. Fruit sorbitol and sucrose contents were not affected by Di and PRD50. Higher glucose in fruit juice was observed in PRD50 (23%) and DI (21.5%) compared to FI, which had the highest malic acid content (33.5-37%). Quinic and citric acids decreased with DI and PRD50, while almost all individual phenolic compounds increased with deficit irrigation. Hydroxycinnamates and anthocyanins were significantly higher in fruits harvested from DI and PRD50 treatments. Proanthocyanidins (catechin and epicatechin) were only improved by DI, while flavone compounds and vitamin C were not affected by irrigation restrictions. ß-carotene was higher in fruits yielded under FI (0.71 mg/100 g DM) than DI and PRD50 (0.21-0.43 mg/100 g DM). Macro- and micronutrients significantly increased in DI and PRD50 fruit. A significant difference between DI and PRD50 fruits was observed for Zn and Fe concentrations. This research highlights the positive impact of reduced irrigation on bioactive-fruit quality attributes and the suitability of PRD50 and DI as tools for irrigation management in arid areas of southern Tunisia, contributing to water-saving in orchards and the improvement of fruit commercial value.

Climate change threatens central Tunisian nut orchards.

Temperate deciduous trees can only be productive where winters are cold enough to meet their chilling needs. In the Mediterranean region, chill has traditionally been sufficient for many species, but this may change as temperatures increase. We explored the region's present and future suitability for temperate trees by quantifying chill for the Sfax region in central Tunisia, one of the warmest regions where temperate nuts are commercially grown. We assessed climatic risk by calculating historic chill (since 1973) and using a weather generator calibrated with local weather data (1973-2015) to produce 101 years of chill estimates (computed with the Dynamic Model) and 3 past and 72 future scenarios (for 2041-2070 and 2071-2100, using two representative concentration pathways: RCP4.5 and RCP8.5). For almonds and pistachios, we compared available chill during the chilling period with the species' estimated chilling requirements, and we computed the date by which sufficient chill was expected to have accumulated. Our findings indicated severe chill losses for all future scenarios. For all species, the current chill period is no longer expected to be sufficient for meeting chilling requirements in the future. Chill needs may still be fulfilled later in the year, especially for low-chill almonds, but this would result in delayed phenology, with possible adverse effects on productivity. Temperate nut production is thus unlikely to remain viable at this site, highlighting an urgent need to identify locally appropriate adaptation options. This challenge is likely shared by other warm production regions of temperate fruits and nuts around the world.

Pistachio (Pistacia vera L.) is a new natural host of Hop stunt viroid.

Besides hop, Hop stunt viroid (HpSVd) infects many woody species including grapevine, citrus, peach, plum, apricot, almond, pomegranate, mulberry and jujube. Here, we report the first detection of HpSVd in pistachio (Pistacia vera L.). Samples corresponding to 16 pistachio cultivars were obtained from a nearby almond collection. From these samples, low molecular weight RNAs were extracted for double polyacrylamide gel electrophoresis, northern-blot analysis and reverse transcription polymerase chain reaction assays. HpSVd was detected in 4 of the 16 pistachio cultivars in the first year and in 6 in the second, being also detected in the almond collection. Examination of the nucleotide sequences of pistachio and almond isolates revealed 13 new sequence variants. Sequences from pistachio shared 92-96 % similarity with the first reported HpSVd sequence (GenBank X00009), and multiple alignment and phylogenetic analyses showed that one pistachio isolate (HpSVdPis67Jabari) clustered with the plum group, whereas all the others clustered with the hop, and the recombinants plum-citrus and plum-Hop/cit3 groups. By identifying pistachio as a new natural host, we confirm that HpSVd is an ubiquitous and genetically variable viroid that infects many different fruit trees cultivated worldwide.

Evaluation of cultivar susceptibility and storage periods towards aflatoxin B1 contamination on pistachio nuts.

Aflatoxins (AFs) are potent sources of health risks to both humans and animals. Among them, AFB1 is the most hazardously toxic and the most frequent in various food commodities, including pistachio nuts. In this survey, the effect of the storage period on AFB1 accumulation on pistachio nuts was investigated. A total of 49 samples collected during the crop year of 2005 from the most cultivated pistachio cultivars in Tunisia were rapidly screened by enzyme-linked immunosorbent assay (ELISA) combined with an immunoaffinity step. The obtained results showed that the contamination of pistachio nuts has occurred clearly after two years of storage for all the tested cultivars except the case of Mateur variety and Thyna ecotypes. In this study, the cultivar Mateur was found to be the most susceptible cultivar to contamination by AFB1. After 4 years of storage, the average contamination levels in nut samples ranged from 2.7 ± 0.3 to 12.7 ± 2.2 µg/kg for AFB1, according to the cultivar. These levels exceeded the maximum permitted limit of 2 µg/kg set by the European Commission in nuts.