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Root-knot nematodes of the genus Meloidogyne are recognised worldwide as a major production constraint in crops of primary economic importance. Knowledge of their diversity and prevalence, as well as the major environmental and agronomical cues for understanding their distribution in specific areas is of vital importance for designing control measures to reduce significant damage. We provide the first detailed information on the diversity, distribution and levels of Meloidogyne species infecting wild and cultivated olive soils in a wide-region in southern Spain that included 499 sampling sites. Overall Meloidogyne spp. were found in 6.6% of sampled olive plants, with 6.6% and 6.5% for cultivated and wild olive, respectively. We identified five previously described Meloidogyne spp. (Meloidogyne arenaria, M. baetica, M. hapla, M. incognita, M. javanica) and one new species (Meloidogyne oleae sp. nov.) which, characterized using integrative taxonomy, increases the known biodiversity of Meloidogyne spp. affecting olive. Meloidogyne arenaria and M. incognita were only found infecting cultivated olive varieties, while, M. baetica was only found infecting wild olive. Three major parameters drive the distribution of Meloidogyne spp. in cultivated olives in southern Spain, cover vegetation on alley, irrigation and soil texture, but different species respond differently to them. In particular the presence of M. incognita is highly correlated with sandy loamy soils, the presence of M. javanica with irrigated soils and cover vegetation, while the presence of M. arenaria is correlated with the absence of cover vegetation on alley and absence of irrigation. These parameters likely influence the selection of each particular Meloidogyne species from a major dispersal source, such as the rooted plantlets used to establish the orchards. [ABSTRACT FROM AUTHOR]

Many studies have analyzed the impact of climate change on crop productivity, but comparing the performance of water management systems has rarely been explored. Because water supply and crop demand in agro-systems may be affected by global climate change in shaping the spatial patterns of agricultural production, we should evaluate how and where irrigation practices are effective in mitigating climate change effects. Here we have constructed simple, general models, based on biological mechanisms and a theoretical framework, which could be useful in explaining and predicting crop productivity dynamics. We have studied maize in irrigated and rain-fed systems at a provincial scale, from 1996 to 2009 in Spain, one of the most prominent “hot-spots” in future climate change projections. Our new approach allowed us to: (1) evaluate new structural properties such as the stability of crop yield dynamics, (2) detect nonlinear responses to climate change (thresholds and discontinuities), challenging the usual linear way of thinking, and (3) examine spatial patterns of yield losses due to water constraints and identify clusters of provinces that have been negatively affected by warming. We have reduced the uncertainty associated with climate change impacts on maize productivity by improving the understanding of the relative contributions of individual factors and providing a better spatial comprehension of the key processes. We have identified water stress and water management systems as being key causes of the yield gap, and detected vulnerable regions where efforts in research and policy should be prioritized in order to increase maize productivity. [ABSTRACT FROM AUTHOR]