Effect of a grey hail protection net on the fruit quality of the 'Bluecrop' highbush blueberry (Vaccinium corymbosum L.)

Abstract

The main focus of our study was to investigate effects of the modified microclimate under a grey hail protection net (HPN) on biometrical fruit characteristics (fruit weight, index of fruit shape, and seed number per fruit) and nutritional value (soluble solid content - SSC, titratable acidity - TA, total anthocyanins - TACY, total phenolics - TPH and total antioxidant capacity - TAC) of the 'Bluecrop' highbush blueberry (Vaccinium corymbosum L.). The study was conducted in the 'Bluecrop' highbush blueberry plantation located in Mladenovac (Serbia) during two consecutive years (2013, 2014). The orchard was established using two-year-old nursery trees in spring 2011, at a planting density of 3,300 bushes per ha. The grey polyethylene net (SILVERLUX®, Helios Group, Lurano, Italy) with a Leno wave structure and a mesh size of 2.8 x 8 mm was used. During the research period, light intensity was measured weekly at 12.00 hr using a digital lux-meter 'Peak teck' PT-5025 (Germany). Air temperature and relative humidity within the canopy were recorded using climate dataloggers (type DT-171, Shenzhen Flus Technology Co., Ltd, China) both under HPN and in the open field (OF). Twelve readings per treatment were taken at 2-hour intervals every day in each season. In both years of observation, light was reduced by 5-20% under HPN, whereby daily maximum temperature was 2.4°C lower causing 4% higher daily minimum relative air humidity than in OF. 'Bluecrop' had significantly higher average fruit weights under HPN ranging from 1.93 g (2013) to 1.86 g (2014) in comparison to those observed in OF. The SSC did not differ between the treatments in 2014, whereas a significantly higher mean value was registered in the fruits harvested under HPN (12.8%) compared to those from OF in 2013. The mean TA was higher under HPN in 2014 (0.57%), whereas in 2013 a significantly higher TA content was found in OF (0.87%). HPN showed a positive effect on the TPH content (7.12 mg GA/g FW), but an almost 2-fold higher value was registered in 2013. Similar to this, TAC was 2.5-fold higher in 2013, without a significant effect of HPN in both experimental years.

U ovom radu su ispitivani efekti izmenjene mikroklime pod sivom protivgradnom mrežom (PGM) na fizičke osobine ploda (masa ploda, indeks oblika ploda i broj semenki u plodu) i nutritivnu vrednost (sadržaj rastvorljive suve materije - RSM, ukupnih kiselina i ukupnih fenola, kao i ukupni antioksidativni kapacitet ploda) sorte borovnice "Bluecrop" (Vaccinium corymbosum L.). Ispitivanja su izvedena u periodu 2013-2014. godina, u zasadu borovnice koji se nalazi u blizini Mladenovca. Zasad je podignut u proleće 2011. godine sa trogodišnjim sadnicama i gustinom sadnje od 3.300 žbunova po ha. Primenjena je siva PGM (SILVERLUX®, Helios Group, Lurano, Italy), težine 48 g/m2, sa veličinom otvora 2,8 x 8 mm. Tokom perioda ispitivanja, intenzitet svetlosti je meren jedanput nedeljno u 12 h korišćenjem luks metra "Peak teck" PT-5025 (Germany). Temperatura i relativna vlažnost vazduha su merene uređajem za evidentiranje podataka (engl. data logger, DT-171, Shenzhen Flus Technology Co., Ltd, China) na svaka 2 h pod PGM i na otvorenom polju (kontrolni tretman) od početka cvetanja do kraja zrenja borovnice u obe ispitivane godine. Intenzitet svetlosti pod PGM je bio u proseku smanjen za 5-20% u obe eksperimentalne godine. Dnevne maksimalne temperature bile su za 2,4 oC niže pod PGM uslovljavajući za 4% višu minimalnu dnevnu relativnu vlažnost vazduha u poređenju sa otvorenim poljem. Značajno veća prosečna vrednost mase ploda kod ispitivane sorte borovnice registrovana je pod PGM u poređenju sa otvorenim poljem, i kretala se od 1,93 g (2013) do 1,86 g (2014). Sadržaj RSM se nije značajno razlikovao između tretmana u 2014. godini, dok je u 2013. godini značajno povećanje registrovano u plodovima koji su ubrani pod PGM (12,8%) u poređenju sa otvorenim poljem (11,6%). Prosečna vrednost sadržaja ukupnih kiselina je bila veća pod PGM u 2014. godini (0,57%), dok je u 2013. godini značajno veći sadržaj pronađen u plodovima ubranim na otvorenom polju (0,87%). PGM je ispoljila pozitivan efekat na sadržaj ukupnih fenola (7,12 mg galne kis. g-1sv.m.pl.), međutim skoro dva puta viša vrednost je bila registrovana u 2013. godini. Slično sadržaju ukupnih fenola, ukupni antioksidativni kapacitet ploda je bio za 2,5 puta veći u 2013. godini, bez značajnog uticaja PGM u obe ispitivane godine.