In a soilless long-term salt-stress experiment, we tested the differences between the commercial sweet pepper cultivar “Quadrato d’Asti” and the landrace “Cazzone Giallo” in the structure and function of PSII through the JIP test analysis of the fast chlorophyll fluorescence transients (OKJIP). Salt stress inactivated the oxygen-evolving complex. Performance index detected the stress earlier than the maximum quantum yield of PSII, which remarkably decreased in the long term. The detrimental effects of salinity on the oxygen evolving-complex, the trapping of light energy in PSII, and delivering in the electron transport chain occurred earlier and more in the landrace than the cultivar. Performance indexes decreased earlier than the maximum quantum yield of PSII. Stress-induced inactivation of PSII reaction centers reached 22% in the cultivar and 45% in the landrace. The resulted heat dissipation had the trade-off of a correspondent reduced energy flow per sample leaf area, thus an impaired potential carbon fixation. These results corroborate the reported higher tolerance to salt stress of the commercial cultivar than the landrace in terms of yield. PSII was more affected than PSI, which functionality recovered in the late of trial, especially in the cultivar, possibly due to heat dissipation mechanisms. This study gives valuable information for breeding programs aiming to improve tolerance in salt stress sensitive sweet pepper genotypes.

Variable rainfall, water stress, and spring frost are the main challenges for cereal growers in the Mediterranean region. The potential of wheat and barley to adapt to contrasting weather conditions was investigated through the adoption of no-till, supplemental irrigation and drought tolerant cultivars over a period of three years. Seasonal precipitation was 732, 336 and 685 mm in the first, second and third seasons, respectively. The second and third seasons were characterized by the occurrence of spring frost. No tillage did not affect productivity in either crop, while supplemental irrigation increased yield only in barley. For wheat, the grain yield was 60 and 43% respectively lower in the second and third seasons than in the first season. For barley, grain yield was 43% higher in the first season than the other two. The negative effect of frost on wheat yield was indirectly assessed by crop growth simulation. Principal component analysis shows that freezing temperatures associated with spring frost and rainfall both dictated crop growth and productivity.

Tomato and pepper leaves were clipped with black leaf clips for dark adaptation under solar radiation in the late spring or early summer 2010 in southern Italy. The leaves showed highly variable maximum PSII quantum yield (F_v/F_m = 0.026−0.802) using a continuous-excitation fluorometer Pocket PEA. These results were confirmed using the modulated fluorometer FMS1 on tomato leaves in mid summer, with F_v/F_m as low as 0.222 ± 0.277 due to nearly equal minimum (F_o) and maximum (F_m) fluorescence emission. A significant clip effect on F_v/F_m occurred after only 12 (tomato) or 25 (pepper) min. Increasing the leaf temperature from 25 to 50°C reportedly induced an F_o increase and Fm decrease so that F_v/F_m approached zero. The hypothesis that black leaf clips overheated under intense solar irradiance was verified by shrouding the clipped leaves with aluminum foil. In clipped leaves of pepper, F_v/F_m with the black clip/Pocket-PEA was 0.769 ± 0.025 (shrouded) and as low as 0.271 ± 0.163 (nonshrouded), the latter showing a double F_o and 32% lower F_m. An 8% clip effect on F_v/F_m was observed with the white clip/FMS1. To avoid the clip effect in high irradiance environments, F_v/F_m measurements with black clip/Pocket PEA system required leaf dark adaptation with radiation-reflecting shrouds. It would be useful if manufacturing companies could develop better radiation-reflecting leaf clips for the Pocket PEA fluorometer.