Possibilities of cucumber powdery mildew detection by visible and near-infrared spectroscopy

I. Alsiņa¹*, G. Bimšteine¹, L. Dubova¹, J. Kaņeps¹, K. Kviesis², B. Bankina¹, M. Dūma³ and A. Avotiņš²

¹Latvia University of Life Sciences and Technology, Faculty of Agriculture, Institute of Plant and Soil Science, Liela street 2, LV-3001 Jelgava, Latvia
²Riga Technical University, Faculty of Power and Electrical Engineering, Kaļķu street 1, LV-1658 Riga, Latvia
³Latvia University of Life Sciences and Technology, Faculty of Food Technology, Department of Chemistry, Liela street 2, LV-3001 Jelgava, Latvia
*Correspondence: Ina.Alsina@llu.lv

Abstract:

Cucumbers are one of the most demanded and widely grown greenhouse vegetables. Important factors that influence quality and quantity of yield are diseases. Powdery mildew (caused by Podosphaera xanthii and/or Golovinomyces cichoracearum), is one of the most harmful cucumber diseases. Early detection of mildew via non-destructive methods can optimize schemes of fungicide application. The study aimed to find regularities in the reflected light spectra, indices described in the literature, and severity of mildew. Plants were grown in the polycarbonate greenhouse under artificial lighting in a 16 h photoperiod with PAR at the tips of plants 200 ± 30 µmol m^-2 s^-1. Leaf reflection spectra were obtained using spectroradiometer
RS-3500 (Ltd. Spectral Evolution). Spectral range 350–2,500 nm, bandwidth 1 nm. The severity of cucumber mildew was evaluated using 10 point scale (0- no symptoms, … 9 – the plant is dead). The vegetation indices found in the literature have been calculated. The obtained results show that the calculated indices have different sensitivities. The strongest correlation between the degree of cucumbers infection with powdery mildew and the light reflectance spectrum was found in the green range of visible light around 550 nm. Disease-Water Stress Index-2 (DSWI-2), Structure Intensive Pigment Index (SIPI), and Normalized Difference Vegetation Index (NDVI) are the most suitable indices for determining powdery mildew in cucumbers. New indices for detection of powdery mildew have been created. None of the studied indices allows determining the powdery mildew at the early stages of disease development when powdery mildew severity is below 10%.

Key words:

Cucumis sativus, DSWI, Golovinomyces cichoracearum, NDVI, Podosphaera xanthii, SIPI

Lighting source as cause of changes in cucumbers’ physiology and morphology

I. Alsiņa¹*, L. Dubova¹, M. Dūma², I. Erdberga¹, I. Augšpole¹, D. Sergejeva¹ and A. Avotiņš³

¹Latvia University of Life Sciences and Technologies, Faculty of Agriculture, Institute of Plant and Soil Science, Liela street 2, LV-3001 Jelgava, Latvia
²Latvia University of Life Sciences and Technologies, Faculty of Food Technology, Department of Chemistry, Liela street 2, LV-3001 Jelgava, Latvia
³Riga Technical University, Faculty of Power and Electrical Engineering, Kaļķu street 1, LV-1658 Riga, Latvia
*Correspondence: Ina.Alsina@llu.lv

Abstract:

The demand of fresh fruits and vegetables is growing. Therefore cultivation of them is essential all year round. The growth in the dark period of a year is not imaginable without artificial lighting sources. Therefore the experiments were carried out to investigate the effects of three different lighting sources on the growth of cucumbers at the early stages of development. Plants were grown in the polycarbonate greenhouse under three different lighting sources: Led cob Helle top LED 280, induction lamp and high pressure sodium lamp Helle magna. Cucumbers were grown in 16h photoperiod with PAR at the tips of plants 200 ± 20 μmol m^-2 s^-1. Plant growth parameters, specific leaf area, pigments, phenols and flavonoids content in leaves, leaf light reflection parameters were determined. Results showed that cucumber plants grown under Led cob Helle top LED 280 in average were smaller, with less chlorophyll, carotenoids and phenols, but leaves have higher chlorophyll a and b ratio and specific leaf area in comparison with traditionally used in greenhouses High Pressure Sodium Lamps (HPSL). Cucumber plants grown under Induction lamp in average were shorter, but with larger leaf area, with higher chlorophyll and carotenoids content, but decreased phenols content in comparison with HPSL. Lichtenthaler index 1 (LIC1) and NDVI are useful for assessing the physiological state of cucumber plants. Despite the fact that the plants grow well and develop normally under all lamps, the results show that sodium lamps are the most suitable for cucumbers. Further research is needed to adjust LED lighting for cucumber cultivation.

Key words: