Pavlos Tsouvaltzis

Boron toxicity effects on grafted and non-grafted pepper (Capsicum annuum) plants

Grafting is a vegetative plant propagation technique. In a grafted plant, the upward supply of water and mineral nutrients as well as the downward flow of photosynthesis are modified. In this context, the objectives of this work were to find out whether the grafting of pepper plants (Capsicum annuum L. family Solanaceae) reduces leaf boron concentration of some commercial cultivars under boron toxicity and to examine the effects of grafting and scion-cultivars on the levels of phenols, flavonoids and antioxidant capacity. Ungrafted plants of the cultivars Century, Twingo, Imperial and Arlequin, as well as grafted Twingo, Imperial and Arlequin plants as scions, and Century as rootstock were used. The plants were treated with 5 mg L-1 boron for 7, 14, 21 and 28 days. After 21 and 28 days of treatment, grafting significantly reduced the boron concentration in the leaves of the scion-cultivars while it was increased by 80% in the non-grafted plants. After 21 days of boron treatment, it was found that grafting reduced the concentration of leaf phenol to 60-70% in ungrafted Century plants. In Century x Twingo there was a 33% increase in the flavonoid concentration of leaves after 7 days grafting; while in the Century x Imperial and Century x Arlequin combinations this was decreased by 75-92% compared to non-grafted Century plants. The antioxidant capacity of leaves after 21 days treatment increased in all rootstockscion combinations by 28% as measured by the FRAP and DPPH methods. In conclusion, grafting reduced boron concentration in the leaves of the tested scion-cultivars, as well as having an effect on the phenol and flavonoid concentrations and antioxidant capacity of the leaves.

Automatic Detection of Different Harvesting Stages in Lettuce Plants by Using Chlorophyll Fluorescence Kinetics and Supervised Self Organizing Maps (SOMs)

Agriculture aims at increasing production and provision of high quality products to the market. Most of the times, quality is strongly correlated with harvesting stage of each product. Specifically, lettuce qualitative characteristics and nutrients appear to vary strongly in different development stages. In 46, 60 and 70 days of growth, the plants were harvested at baby, immature and mature stage. Then, the parameters of chlorophyll fluorescence were determined in two middle leaves of 3 plants of each hybrid at different harvest stage by using chlorophyll fluorescence kinetics. The measurements revealed significant differences between harvesting stages. The fluorescence parameters were utilized as inputs for training different models of supervised Self Organizing Maps (SOMs) aiming at the prediction of harvesting stage. It was shown that the prediction of different harvesting stages is h by supervised SOMs due to non-linearity nature of the problem which is owned to the heterogeneity of the fluorescence kinetics parameters.

WOUND-INDUCED RESPIRATION AND ETHYLENE PRODUCTION IN FRESH CUT ROMAINE LETTUCE

Understanding of the physiological and biochemical processes induced by cutting can help in devising strategies to improve fresh-cut lettuce quality. We evaluated the response of Romaine lettuce to cutting temperature by cooling overnight and processing five, freshly harvested heads at 5 or 15°C. Undamaged, expanded leaves were immersed for 1 min in 5 or 15°C chlorinated water (1.34 mM NaOCl; pH 7), cut in half longitudinally then cut transversely into 2-cm wide pieces, the cut pieces were re-immersed in chlorine solution, and the excess liquid removed with a salad spinner. Cut pieces from each head (100 g) were measured in flow-through systems every 2 h for 24 h for O2, CO2, and C2H2 by gas chromatography. The CO2 evolution immediately after cutting was approximately 3.5-fold higher at 15°C than at 5°C, and O2 consumption was approximately 2.2-fold higher at 15°C. The CO2 evolution at 15°C increased during the first 4 h after cutting and thereafter remained steady; at 5°C, a small increase occurred during the first 8 h with a slight decline thereafter. The O2 consumption at 15°C increased during the first 3 h after cutting, decreased until hour 10, then remained steady or declined slowly. The O2 consumption at 5°C decreased by half during the first 12 h after cutting and changed little thereafter. The respiratory quotient (RQ) was <1.0 during the first 8-12 h after cutting, rose and remained steady at approximately 1 for 8-10 hours at 5°C and for about 8 h at 15°C, then finally increased to about 1.1 at 5°C and 1.7 at 15°C. Ethylene production was 6-fold higher at 15°C than at 5°C and did not change over time. These relative changes in CO2 production and O2 consumption suggest that non-respiratory oxidative reactions play a significant role in the post-cutting wound response of fresh-cut lettuce.