To clarify the effect of reflective sheet mulching on photosynthesis of fruit tree canopies, we investigated, in sweet cherry and pear orchards, the photosynthetic photon flux density (PPFD) reflected from sheet-covered ground, the difference in net photosynthetic rate (Pn) between sheeted and unsheeted (control) plots, and the effects of long-term mulching on leaf character and fruit quality. In complementary greenhouse experiments, we investigated thePn of leaves illuminated by various combinations of a range of artificial PPFDs at the abaxial and abaxial surfaces. Though the maximum reflected PPFDs from the control plots distributed below 10μmol m-2s-1in the cherry and 20μmol m-2s-1in the pear, those from the sheeted plots were around 200 μmol m-2s-1. Combining these results with those obtained in the greenhouse experiments led us to estimate that the mean increment ofPnprovided by mulching would be about 2.1 μmol CO2m-2s-1for cherry and about 3.2 μmol CO2m-2s-1for pear. The observed increments ofPnin the lower leaf layers of mulched trees were discussed. Long-term mulching resulted in leaves with sun leaf character and improved the coloring of cherry fruit, though there was no difference in fruit size between the mulched and unmulched plots for either cherry or pear.
We developed an automatic digital imaging system to acquire sequential growth images of rice in tillering stage. In this system, we cultivated 24 plants and acquired images of each individual plant at one-hour intervals. We measured leaf height using this system for 36 days from these sequential images. These sequential leaf height measurements made it possible to quantify the precise growth of rice plants, showing the timing of leaf elongation, leaf emergence interval and leaf elongation rate. We applied this method to evaluate the effect of photoperiod and tem-perature on rice growth. The timing of leaf emergence and the leaf emergence interval were affected by temperature and day length. On the other hand, the maximum leaf elongation rate was not significantly different under the temperature and day length examined. These results suggest that temperature and day length have different effects on leaf emergence and leaf elongation in rice. This method and instrument could be applied to phenotypic profiling studies for comprehensive growth of various plants species and cultivars.
In order to develop the feasible fertigation system, tomatoes “Momotaro Fight” were grown in bag culture system with drip irrigation equipments using coconut coir as substrate. The growth stage was separated into 5 stages for supply different amounts of nutrients and water. In this sys-tem the setting amount of nutrient was supplied when the cumulative solar radiation (CSR) value reached 1 MJ m-2. The setting amounts increased gradually (from 0.23-0.40 me plant-1MJ-1m2) with the process of growth stage. There were 4 treatments with varying levels of water supply for vapor pressure deficit (VPD) as follows: V-0 (no additional supply of water), V-20, V and V+20. In the V-0 treatment, the highest contents of total soluble solids in the fruits were re-corded, while the values of the leaf dry weight, photosynthetic rate and yield were the lowest. The V and V+20 treatments were associated with a lower percentage of drainage (5-7%), higher water use efficiency and nitrate use efficiency while salt accumulation inside the substrate could be avoided. With these 2 treatments a highly efficient fertigation system based on CSR and VPD values was developed for the production of low truss tomato production system.
Tomatoes (cv. “Momotaro Fight”) were grown in a bag culture with a drip irrigation system using coconut coir as a substrate. An efficient fertigation management system using integrated solar radiation and vapor pressure deficit (VPD) were conducted in order to confirm the efficiency of the system and to obtain the data of transpiration rate (E) . With this system nutrients and water were supplied when the cumulative solar radiation (CSR) reached a value of 1 MJ m-2, setting the supply volume (per 1 plant-1MJ-1m2) was gradually increased depending on the growth stages. TheEvalue of tomato was measured using a weighing lysimeter. TheEdata obtained from the V-100 treatment which was associated with the highest water and nitrate use efficiency, were used to perform linear regression equation for the estimation ofEvalue relating either VPD and/or CSR. The linear regression equation ofEvalue fitted moderately well with both VPD and CSR. Therefore, a more suitable fertigation system could be developed based on the estimation of theEvalue with VPD and CSR values. Moreover, the linear regression equation obtained could be applied for developing fertigation management system in tomato bag culture under wide range of greenhouse conditions.
The objectives of this study were to investigate the effect of short-term changes in the spectral environment on photosynthesis. Lettuce (Lactuca sativa) plant were grown under red-greenblue (RGB) light-emitting diodes (LEDs) for 23 d and then given 24-h exposure to red (R), redgreen (RG), or red-blue (RB) LEDs. Photosynthetic rates (Pn) were measured before the 24-h exposure, after 24-h exposure, and 24 h after returning to the original RGB lighting. Temporary changes in spectral quality affectedPn. The effects of the different light treatments onPnreversed after returning to the initial light source. This study showed thatPnwas responsive to spectral quality in the short-term and is not directly coupled to stomatal conductance.
Ethylene induces premature senescence of orchid flowers when plants are particularly transported with fruits and vegetables stored nearby. Exogeneous ethylene regulated a complex physiological changes of petals in intact flowering clones ofDendrobium phalaenopsisduring seven days; decrease in distance between petals, water content, NMR relaxation times (T1sandT2s) and degree in vital staining, while increase in ion leakage and translucence. Petal wilting and decrease in water content in florets were closely correlated with loss in viability of petal parenchyma tissues adjacent to the vascular bundles in the ethylene-exposed orchid flowers. Highly mobile water measured by T1values of the long fraction in the petals was considered to free water derived from intact vacuoles. The loss of membrane integrity and free water of the orchid petals can be modulated by ethylene. After ethylene exposure treatment, the free water gradually decreased at 5 d. Additionally, T2s of the short fraction in the petals markedly decreased at 5 d after the ethylene exposure and they reached to 10 ms at 7 d. From these results, the decrease in the T1 and T2of the orchid petals due to ethylene exposure indicated decreased vacuolar water, followed by turgor loss and increased bound water, thus decrease in diffusion of substrates and metabolism.
Pre-harvest sprouting (PHS) is a serious source of costly yield and grade losses for producers. Unreleased test lines of cereals should be screened for resistance to PHS. However, screening large numbers of test lines is relatively time-consuming or expensive. In this study, nuclear magnetic resonance (NMR) was used to characterize PHS as a nondestructive method. The water content in the rice grains of ‘TC65’ and ‘Notched’ gradually decreased until 21 days after pollination (DAP) . After 21 DAP, the water content in both lines remained constant. In PHS at this time, none of the ‘TC65’ seeds germinated while 15% of the ‘Notched’ seeds had germinated. At 14 DAP when PHS was not confirmed, NMR spin-spin relaxation time (T2) in ‘TC65’ and ‘Notched’ seeds were about 40 ms and 20 ms, respectively. These results indicated that the T2 is effective to screen resistance to PHS at early stage. In addition, T2s in germinating seeds linearly increased to 165 ms as germination advanced during 10-day treatment period. On the contrary, T2s in nongerminating seeds were about 20 ms and they remained constant during the treatment period. Thus, 1H-NMR relaxation times were measured as a way to screen both resistance to PHS and germination process.
Growth of tomato (Lycopersicon esculentum Mill.) seedlings under low temperature stress was investigated using several cultivars to estimate suitable rootstocks for direct transplanting of plug seedlings under low temperature condition. Plants were grown in a growth chamber at 25°C for 3 weeks, and at 10°C for the following 3 weeks. The increase in dry weight of shoots during the 10°C period showed a maximum in ‘Kagemusya’ followed by ‘Anka-T’, ‘Shin-meito’. ‘Kagemusya’ and‘Anka-T’ had a greater dry weight of roots; both lateral and main roots increased greatly in ‘Kagemusya’ and ‘Anka-T’. The cultivars were divided into high and low groups for the triphenyl-tetrazoliumchloride (TTC) reduction rate of roots under the 10°C condition. The rate was highest in ‘Kagemusya’, ‘Anka-T’ and‘Shin-meito’, all of which had a high increase in the dry weight of shoots. From these findings, it is suggested that the growth of tomato rootstocks under low temperature stress differed with each cultivar, and ‘Kagemusya’ showed the best growth. Hence, ‘Kagemusya’ is considered to be suitable for direct transplanting of tomato plug seedlings especially under low temperature conditions.