Root distribution and water use in coffee shaded with Tabebuia rosea Bertol. and Simarouba glauca DC. compared to full sun coffee in sub-optimal environmental conditions

International audienceRoot niche differentiation for optimal exploitation of resources was found in an arabica coffee agroforestry system in Nicaragua. Rooting behavior was compared in both unshaded (FS) and shaded (AFS) coffee combined with two previously untested tropical timber species (deciduous Tabebuia rosea Bertol. and evergreen Simarouba glauca DC.). The predominant andisol possesses a compacted soil layer (talpetate). The study was conducted in sub-optimal environmental conditions for coffee cultivation (455 m.a.s.l., annual mean 27 A degrees C, 1300 mm rainfall/year, 6 months dry season) in Nicaragua. Twelve and five trenches 200 cm deep were dug in AFS and FS respectively. Roots per unit area were counted on two perpendicular soil faces. Volumetric water was measured continuously over 2 years by using 45 reflectometers in different soil layers. The talpetate varied greatly in depth, thickness and physical structure. Coffee fine roots were more abundant than tree roots and were concentrated in the shallower strata (0-80 cm) whilst tree roots proliferated more below 100 cm. The S. glauca root system was denser below 100 cm than T. rosea root system. There was no meaningful difference in coffee root counts in FS and under T. rosea, but coffee root counts were higher near S. glauca trees. 2012 and 2014 had mild dry seasons and whole profile soil water content was similar in FS and AFS, but in the 2013 severe dry period volumetric water and water uptake were lower in AFS than in FS. This indicates that the normal advantage of greater soil exploration in AFS was cancelled presumably due to continued water uptake by deep rooting trees whereas the FS still had available water

“Flavescence dorée” impacts growth, productivity and ultrastructure of Vitis vinifera plants in Portuguese “Vinhos Verdes” region

“Flavescence dorée” (FD) is a quarantine disease associated with the presence of a phytoplasma transmitted by the insect vector Scaphoideus titanus. This disease affects grapevines and is of a great concern to the stability and sustainability of the wine industry, due to the harvest losses and death of infected plants. In Portugal, FD has seriously affected the “Vinhos Verdes” region, but so far the research on this topic is very limited. The current study confirmed that the FD phytoplasma strain involved in the outbreak in Vitis vinifera cv. Loureiro belongs to the 16SrV-D subgroup and shows very low RFLP variability in the tuf and secY genes. Transmission electron microscopy analysis of leaf midribs from infected grapevine plants revealed that the shape and structure of phloem cells were altered, presenting collapsed cells, callose accumulation in sieve plates and lipid accumulation in chloroplasts of phloem parenchyma cells. Moreover, data from two subsequent years showed that FD presence was associated with an average delay of 10 to 15 days on the time to visible inflorescences and to veraison, compared to healthy plants. At veraison, FD also lead to a significant decrease in the budburst percentage (7% to 12%), fertility index (35% in 2015), leaf area (56% to 63%), and chlorophyll content (18% to 35% lower SPAD values). Hence, infected plants showed a drastic reduction in the yield, corresponding to a decrease between 51% and 92% compared to healthy plants, which mostly resulted from a lower number of bunches (63% to 92% less), but also a decreased bunch weight (35% lower in 2015). Concerning berry quality, there were no significant differences in terms of total soluble solids and titrable acidity in both years. Here, this study concluded that the FD infection delays the grapevine development and leads to drastic production losses, which may be partly linked to the ultrastructural modifications observed in the phloem cells of infected plants.N/