Agriculture and Science 2021/10

Varietal differences in the occurrence of tomato blistering disease are
　　　The ratio of above-ground weight to below-ground weight is involved.

Fukushima University, Faculty of Agriculture, Department of Food and Agricultural Sciences
Yoko Miyama

Introduction

　Tomato blistering is a physiological disorder also known as leaf blistering. In severe cases, the leaves become deformed (Fig. 1c), brownish, and even defoliate (Fig. 1d). Blister blight is said to be caused by changes in the leaf surface layer (Suzuki et al., 2020) and has become a problem in recent years, especially in seedling production sites (Jokan, 2015, Misu et al., 2018).

　The cause of blistering is not clear. There are reports (e.g. Lang, S. P., Tibbitts, T. W. 1983,Eguchi et al. 2016) that it occurs when UV light intensity is low or when high humidity persists. However, in production, outbreaks have been observed even under conditions of high UV intensity and high humidity that do not persist for long periods of time. For example, there have been many cases of outbreaks when dry conditions were followed by a sudden change to wet conditions due to lack of irrigation water or other factors. This suggests that fluctuations in plant water absorption and transpiration are involved in the occurrence of blistering. It has also been shown that the degree of occurrence of blistering depends on the tomato variety (Tsuburaya et al., 2017, Ozawa et al., 2018). Based on the above, it is thought that the proportion of roots that absorb water and above-ground parts of the plant body that transpire may influence the inter-varietal differences in the degree of occurrence.
　Here we would like to present some of the author's research on tomato blistering.

2. EUT type

　The main varieties in Kanagawa Prefecture, 'House Momotaro', 'CF House Momotaro', and 'CF House Momotaro', were used as test varieties.
'CF Momotaro Haruka','Momotaro Peace','Momotaro Hope','Sun Road ','Reijo','Reika','Reijun','TY Misora 86 ', 'Shonan Pomoron Red', and 'Shonan Pomoron Gold'. Seedlings of these varieties were sown and grown in 128-hole cell trays filled with commercial media and tested.

3. interspecific differences in blistering and above-ground dry matter weight/underground dry matter weight

　Differences in the occurrence of blistering were examined by placing 14-day-old seedlings in the closed seedling production system "Seedling Terrace" in an artificial weather chamber at a temperature of 30°C and a relative humidity of 901 TP3T, with continuous bottom feeding. No blistering was observed in the seedlings before the start of treatment.

　As a result, blistering was not observed in 'House Momotaro', 'Momotaro Hope', 'Sun Road', 'Reijo', 'Shonan Pomoron Red', and 'Shonan Pomoron Gold' on the third day of treatment. ', 'Shonan Pomoron Red', and 'Shonan Pomoron Gold' did not develop blister disease on the third day of treatment, while 'Momotaro Peace ', the incidence of blistering disease was 1001 TP3T. On the 6th day of treatment, no outbreak was observed in 'Sun Road', 'Reirao', and 'Shonan Pomoron Gold'. On the other hand, 'CF Momotaro Haruka', 'Reika', 'Reijun', and 'TY Misora 86' showed reached 1001 TP3T. On the 9th day of treatment, 1001 TP3T was reached except for 'Reijo' (Table 1, Fig. 2).

　The aboveground dry matter weight/underground dry matter weight was calculated by weighing seedlings grown for 16 days on the "seedling terrace" as described above after drying the aboveground and underground portions at 60°C. The aboveground and underground portions were then weighed.
　The results showed that the above-ground dry matter weight/underground dry matter weight was the lowest for 'Reirao', followed by 'Shonan Pomoron Red' and 'TY Misora 86'. The weight of 'Reirao' was the lowest, followed by 'Shonan Pomoron Red' and 'TY Misora 86'. On the other hand, 'Momotaro Peace' had the largest dry weight, followed by 'Reijun' and 'House Momotaro' (Figure 3).
　In other words, the smaller the ratio of roots to above-ground parts, the more likely it was that blistering would occur.

4. interspecific differences in water potential variability

　Purchased seedlings (Berg Earth Co., Ltd.) grown in 128-hole cell trays in the "Seedling Terrace" were used for the water potential measurement. Three varieties were used for water potential measurement: "Momotaro Peace," which showed a high degree of blistering in the aforementioned experiment; "CF House Momotaro," which showed a medium degree of blistering; and "Reijou," which showed a low degree of blistering. The three varieties used were 'Momotaro Peace', 'CF House Momotaro', and 'Reiyo'. The temperature was 30°C, relative humidity 50%, and
The tomato seedlings were placed in an artificial weather chamber set up under dry conditions with no liquid supply, and after 24 hours were changed to wet conditions with a relative humidity of 901 TP3T and continuous bottom feeding to examine changes in the water potential values of the tomato seedlings.

　The soil water potential ranged from 78 to 791 TP3T at the beginning of treatment, 37 to 441 TP3T 24 hours later, and 79 to 801 TP3T 2 hours after the start of continuous bottom feeding (26 hours after the start of treatment). Water potential decreased during dry condition in the order of 'Momotaro Peace', 'CF House Momotaro', and 'Reijo'. Then, water potential increased rapidly when the conditions were changed from dry to wet, and there was no significant difference among the three varieties after 26 hours (Figure 4). In other words, it was clear that varieties with higher above-ground/sub-ground weights had a greater tendency to lower water potential during dry conditions and a greater range of rapid increases during wet conditions.

　It was inferred that the development process of blistering was caused by an imbalance between the rate of water absorption from the roots and the rate of transpiration from the leaves, resulting in damage to the leaf surface layer due to swelling pressure.
　When growing seedlings in cell trays, bottom-feeding is often used. In bottom-feeding, soil moisture content increases rapidly during watering. Furthermore, in closed seedling production facilities, the relative humidity also increases rapidly during watering. This suggests that the risk of blistering may be greater in cultivars with a low subsoil weight relative to the above-ground weight.

5. Conclusion

　In the present study, we investigated the cause of blistering by using seedlings grown in a closed seedling production system and found that the water ring
The sudden change in the soil conditions was considered to be a contributing factor to the occurrence of blistering. However, blistering can occur even after planting (Fig.
5). Since the seedlings were not fed from the bottom of the tray as in cell tray seedling growth, changes in the water environment could be caused by other factors.
This is thought to be the cause of the blistering. In addition, the relationship between the ratio of above-ground weight/underground weight after planting and the degree of blister disease occurrence
The results of this study are not yet available. We plan to clarify these issues in the future.

thanks

　We would like to thank Berg Earth Corporation and Hiroyuki Kikuchi for providing the experimental seedlings. This research was supported by JSPS Grant-in-Aid for Scientific Research JP19K06013.

No Soil - No. 5
　　Conditions for Good Soil Physical Properties - Part 4
　　What is soil that holds water adequately and drains well?

Hokkaido Branch Office, JCM Agri Co.
　Teruo Matsunaka Technical Advisor

　The second of the four conditions for good soil, which concerns the physical properties of the soil, is that the soil should "retain a moderate amount of moisture and have moderate drainage. In the previous article, I described how to determine whether the soil drains well or not from the cross-section of the soil. This time, we will consider how soil retains water, the fact that some water in the soil can be used by crops and some cannot, and what kind of soil retains water adequately and drains well.

1. capillary tension is the key to water retention and drainage

　See Figure 1. Two types of glass capillaries of different thicknesses are placed in water dyed with blue ink (hereinafter referred to as "ink"). In both glass capillaries, the surface of the water rises slightly. This is called capillary action, and the force that pulls up the water is capillary tension. The reason why the ink is raised higher in the thinner glass capillary is because the capillary tension is stronger than in the thicker glass capillary.

　When this glass capillary was lifted above the surface of the ink, the ink in the thin glass capillary remained in the capillary, while the ink in the thick capillary fell to the floor (Figure 2). The capillary tension in the thin glass capillary is stronger than that of gravity, and thus water is retained in the capillary. However, the capillary tension in the thick glass capillary is weaker than the downward pull of gravity, and as a result, the ink fell out of the capillary (drainage).

　Let us consider this in terms of the gaps in the soil. The space between particles in soil is composed of small, thin gaps and large, thick gaps. Sandy soil with coarse grains (coarse-grained soil) has fewer small gaps and more large gaps, so the capillary tension in the gaps is weak and water tends to drain out. This results in poor water retention, which can lead to drought damage to crops. On the other hand, fine-grained and cohesive soil (fine-grained soil) has many small gaps and few large gaps, so the capillary tension in the gaps is strong. Therefore, water is retained in the narrow gaps, resulting in poor drainage.

2. water that can and cannot be used by crops

　Imagine that there has been a very heavy rainfall and that all the crevices in the soil have been filled with water. There is no space for air to enter the soil, and there are only soil particles and water. The amount of water in the soil at this time is called the "maximum water capacity. However, about 24 hours after the rain stops, the water that was held in the thick crevices by a force weaker than gravity is pulled down by gravity and drains away. Air enters the gap where the water has been drained away. The amount of water in the soil at this time is called the "field water capacity. Of course, the drained water cannot be absorbed and used by the crop.

　If there is no rain for a while after this condition, the soil dries out. As the dryness progresses, the crop wilts, even though there is no water in the soil at all. At this time, it is often experienced that the wilting is restored by watering. However, if the dryness continues without water, the crop withers and dies. However, even in such a case, the water in the soil has not completely disappeared. The amount of water in the soil at this time is called the "permanent wilt point" (wilt means to wilt). The water in the soil at this time is held in very fine crevices and clay (soil particles finer than 0.002 mm in diameter) with a force greater than the water absorption capacity of the crop roots. Therefore, even though the soil has not completely run out of water, the crop cannot absorb the water and withers and dies.

　Ultimately, the amount of moisture that is available to the crop in the soil is the amount of moisture at the permanent wilting point minus the amount of moisture at the field capacity, which is the state after drainage is completed. This moisture available to the crop is called effective moisture. The water remaining in the soil at the permanent wilting point is called invalid moisture because it is not available for crops.

3. soil type and effective moisture content

　Soil grain size and effective moisture content are very closely related (Figure 3). Coarse-grained soil has many large, thick crevices and good drainage, resulting in low water content at field capacity (Figure 3). As the soil grains become finer, the amount of water held in the soil increases due to the increase in the number of small crevices, and the amount of water in the field water capacity also increases. However, when the soil grains become finer to a certain degree, the large gaps related to drainage do not change, so the field water content does not change significantly even if the soil grains become finer, and the field water content reaches a ceiling (Figure 3).

　On the other hand, the amount of water in the soil when the crop wilts to death, i.e., the amount of water at the permanent wilting point, increases linearly with finer soil grains (Figure 3). This is because the finer the soil grains, the more clay content and very fine crevices there are, and the greater the amount of moisture that is strongly retained there. Therefore, the effective water content, which is the difference between the field water content and the permanent wilting point, is greatest in medium-grained soils (Figure 3).

4. soil with reasonably good drainage and water retention and how to determine this

　Medium-grained soil is neither extremely coarse-grained nor extremely fine-grained. Medium-grained soil has both large gaps for drainage and small but not too fine gaps for water retention. This moderate proportion of crevices produces a soil that drains well and retains a large amount of effective water content.

　To determine if the soil is medium-grained, knead the moist soil with your thumb and forefinger and stretch it into a thread. The soil can be considered medium-grained if it can be stretched to the thickness and length of a matchstick, but not beyond that. If the soil is not matchstick-like, but rather difficult to form threads, it is considered coarse-grained soil.

5. the size of soil particles cannot be easily changed

　We know that medium-grained soils are reasonably good for drainage and water retention. However, the size of the soil particles is determined by the degree of weathering of the rocks from which the soil is made, which requires time enough to tell the geologic age of the soil. Turning coarse- or fine-grained soil into medium-grained soil is not something that can be done overnight. Creating gaps in the soil for water retention and drainage requires a generational effort to continue applying organic matter such as compost.