A. Aguado

Molecular Tools for Detection of Plant Pathogenic Fungi and Fungicide Resistance

Plant pathogenic fungi are the causal agents of the most detrimental diseases in plants, including economically important crops, provoking considerable yield losses worldwide. Fungal pathogens can infect a wide range of plant species or be restricted to one or few host species. Some of them are obligate parasites requiring the presence of the living host to grow and reproduce, but most of them are saprophytic and can survive without the presence of the living plant, in the soil, water or air. Isolates of a fungal species can be differentiated by morphological characteristics, host range (formae speciales), pathogenic aggressiveness (pathotypes or races) or their ability to form stable vegetative heterokaryons by fusion between genetically different strains (belonging to the same vegetative compatibility group, VCG).

Towards the Improvement of Fruit-Quality Parameters in Citrus under Deficit Irrigation Strategies

Water shortage is becoming a severe problem in arid and semiarid regions worldwide, reducing the availability of agricultural land and water resources. In Spain, citrus is one of the most economically important crops, with 74,000 ha devoted to its cultivation. Since water resources are increasingly more insufficient, the efficient use of water is becoming more essential. Deficit irrigation in many agricultural crops has frequently proved to be an efficient tool for improving water-use efficiency. This paper examines the effects a deficit irrigation during the ripening period on yield and the most representative fruit quality properties. The study was conducted during two consecutive years (2009-2010) in a commercial 12-year-old orange orchard (Citrus sinensis L. Osb. cv. Navelina) grafted onto Carrizo citrange (Citrus sinensis L. Osb. × Poncirus Trifoliata L. Osb.). A regulated deficit irrigation (DI) was applied, which was fully irrigated during the flowering and fruit-growth stage, and during the ripening period it was subjected to a water-stress ratio of 0.75. A control treatment was established, this being irrigated at 100% of crop evapotranspiration. Along the water stress period, it was tested the temporal evolution of the main organoleptic and nutraceutical fruit properties (color index, the total soluble solids, titrable acidity, maturity index, rind weight, juice weight, the ratio of juice weight versus fruit weight, and the total C vitamin and flavonoids). It was not observed a descend in juice content, or fruit weight, or in the final yield. In terms of fruit organoleptic and nutraceutical properties, there were not detected negative effects in the studied properties. Furthermore, DI treatment showed higher values of maturity index than control treatment, which can be considered as a positive aspect in the fruit quality. Considering these results, we can affirm that a moderate water stress applied during the maturity period is a sustainable strategy for saving water, increasing the irrigation productivity and obtaining fruits with similar properties to those without deficit irrigation.

Physiological and gene expression responses of sunflower (Helianthus annuus L.) plants differ according to irrigation placement

To investigate effects of soil moisture heterogeneity on plant physiology and gene expression in roots and leaves, three treatments were implemented in sunflower plants growing with roots split between two compartments: a control (C) treatment supplying 100% of plant evapotranspiration, and two treatments receiving 50% of plant evapotranspiration, either evenly distributed to both compartments (deficit irrigation - DI) or unevenly distributed to ensure distinct wet and dry compartments (partial rootzone drying - PRD). Plants receiving the same amount of water responded differently under the two irrigation systems. After 3 days, evapotranspiration was similar in C and DI, but 20% less in PRD, concomitant with decreased leaf water potential (Ψleaf) and increased leaf xylem ABA concentration. Six water-stress responsive genes were highly induced in roots growing in the drying soil compartment of PRD plants, and their expression was best correlated with local soil water content. On the other hand, foliar gene expression differed significantly from that of the root and correlated better with xylem ABA concentration and Ψleaf. While the PRD irrigation strategy triggered stronger physiological and molecular responses, suggesting a more intense and systemic stress reaction due to local dehydration of the dry compartment of PRD plants, the DI strategy resulted in similar water savings without strongly inducing these responses. Correlating physiological and molecular responses in PRD/DI plants may provide insights into the severity and location of water deficits and may enable a better understanding of long-distance signalling mechanisms.

Potential Inoculum Sources and Incidence of Strawberry Soilborne Pathogens in Spain

The decline and death of strawberry plants in Spanish fruit production fields have mainly been attributed to the soilborne pathogens Macrophomina phaseolina, Phytophthora cactorum, and Fusarium spp. Inoculum sources of M. phaseolina and P. cactorum, and the incidence all three genera, were investigated in nurseries and fruit production fields over three consecutive seasons. M. phaseolina inoculum sources consisted of fumigated preplant fruit production soils (50%) and fumigated nursery soils (47%), although the pathogen could not be detected in nursery mother and runner plants. P. cactorum inoculum sources included nursery (20%) and preplant fruit production (17%) fumigated soils, and nursery runner plants (up to 15%). In fruit production plants, the average incidence of M. phaseolina and P. cactorum were 4.2 and 3.7%, respectively. Fusarium spp. inoculum sources could not be accessed extensively due to the lack of effective quantitative real-time PCR assays. Limited testing of nursery plants showed that Fusarium oxysporum f. sp. fragariae (Fof) was absent. In field production plants and soil, F. solani was the main pathogenic Fusarium spp., with Fof only identified once in a fruit production plant. Ineffectively fumigated soils in nurseries and production fields, along with infected runner plants, can be inoculum sources of soilborne strawberry pathogens in Spain.