Studies on the lenticel development, surface microflora and infection by common scab (Streptomyces scabies) of potato tubers growing in wet and dry soils

The mechanisms of control of potato common scab (Streptomyces scabies) by irrigation were investigated in 5 years by studying the growth and surface microflora of young potato tubers developing in wet or dry soils. Direct examination of the tuber surface by light or scanning electron microscopy showed that the newly formed internodes near the apex, which carry stomata, had a very sparse microflora. In dry soil the older internodes, which carry lenticels at a susceptible stage, were increasingly colonised by actinomycete hyphae and discrete, although sometimes large, bacterial colonies. In wet soil, actinomycetes were rarely seen on tuber surfaces but bacteria were generally scattered over them, differences not always shown by isolation from periderm pieces onto water agar. When dry scab-infested soil was wetted, scabs did not subsequently develop on the two youngest tuber internodes (A-1, A-2), which may be an example of disease escape rather than inherent resistance of the stomata. The scab control achieved in wet soil was probably caused by some form of microbial antagonism, but whether through competition or antibiosis was not established.     

Susceptibility of potato tubers to infection by Phytophthora infestans

Phytophthora infestans infects King Edward potato tubers more readily through inoculated eyes than through lenticels, but more lenticels than eyes became infected when whole tubers were sprayed with inoculum. The resistance of lenticels but not of eyes increased as tubers aged. The spores did not infect through intact periderm. The likelihood of tubers on plants grown in pots becoming infected by sporangial suspension poured on to the soil increased the nearer the tubers were to the soil surface, the stem, or the side of the pot. Naturally infected tubers, and those sprayed with sporangial suspension, had most eyes infected at the rose end, and most lenticels infected on the middle region of the tuber. Of naturally infected tubers, on which the site of infection could be identified, most were infected through eyes at the rose end.     

Sites of contamination and numbers of Erwinia carotovora present in stored seed potato stocks in Scotland

Forty-eight bulk and crate stored commercial seed potato stocks from the east of Scotland were examined for contamination by Erwinia carotovora in 1967 and 1968. Both E. carotovora var. carotovora and E. carotovora var. atroseptica were present, the latter, the blackleg pathogen, being detected four times more frequently. Most contamination was located on the tuber surface and in the lenticels; it was rare in the vascular ring and the organism was never detected in the cortex. The level of contamination of lenticels was only slightly affected after winter storage, which, however, substantially reduced surface contamination. More than 10³ cells were detected on the surface of tubers in over half the stocks and in half the stocks each lenticel sampled contained more than 10² bacteria.     

Potato tuber lenticels: susceptibility to infection by Erwinia carotovora var. atroseptica and Phytophthora infestans

In laboratory tests, proliferation increased the susceptibility of lenticels on mature tubers to infection by Erwinia carotovora var. atroseptica. No differences in susceptibility to E. c. atroseptica and Phytophthora infestans were detected on tubers lifted at different stages of growth from soil kept wet or dry for 3 wk prior to each sampling. As tubers aged, fewer lenticels became infected by either pathogen or were penetrated by fluorescein dye, presumably because cells had been suberized and cork barriers formed.     

The effect of a few days of rain on the distribution of common scab (Streptomyces scabies) on young potato tubers

At Woburn, Beds, in 1967, potato tubers formed and grew in dry soil except after rain between 23 and 26 June. At lifting, Majestic tubers were severely and uniformly scabbed, except for distinct bands free from lesions. The position of the bands differed depending on the date when tubers started to form; they were further from the stolon attachment when tubers formed early and nearer it when tubers formed late. Samples taken in June and July showed that the scab-free band and the late June rain were related. From 25 June to 1 July the soil was probably wet enough to prevent Streptomyces scabies infection, but only one or two tuber internodes remained free from infection; they were the internodes that began to expand about a week before the rain. Internodes that formed while the soil was wet became scabbed, showing they were still susceptible to S. scabies after the soil had dried again. Recent work on lenticel formation has suggested a hypothesis to explain these results.     

Root distribution in relation to soil nitrogen availability in field-grown tomatoes

Tomato root growth and distribution were related to inorganic nitrogen (N) availability and turnover to determine 1) if roots were located in soil zones where N supply was highest, and 2) whether roots effectively depleted soil N so that losses of inorganic N were minimized. Tomatoes were direct-seeded in an unfertilized field in Central California. A trench profile/monolith sampling method was used. Concentrations of nitrate (NO₃ ^-) exceeded those of ammonium (NH₄ ⁺) several fold, and differences were greater at the soil surface (0–15 cm) than at lower depths (45–60 cm or 90–120 cm). Ammonium and NO₃ ^- levels peaked in April before planting, as did mineralizable N and nitrification potential. Soon afterwards, NO₃ ^- concentrations decreased, especially in the lower part of the profile, most likely as a result of leaching after application of irrigation water. Nitrogen pool sizes and rates of microbial processes declined gradually through the summer.Tomato plants utilized only a small percentage of the inorganic N available in the large volume of soil explored by their deep root systems; maximum daily uptake was approximately 3% of the soil pool. Root distribution, except for the zone around the taproot, was uniformly sparse (ca. 0.15 mg dry wt g^-1 soil or 0.5 cm g^-1 soil) throughout the soil profile regardless of depth, distance from the plant stem, or distance from the irrigation furrow. It bore no relation to N availability. Poor root development, especially in the N-rich top layer of soil, could explain low fertilizer N use by tomatoes.     

The effect of granular nematicide incorporation depth and potato planting depth on potatoes grown in land infested with the potato cyst nematodes Globodera rostochiensis and G. pallida

Field experiments at Harper Adams, Shropshire and Wisbech, Cambridgeshire investigated the effect of nematicide incorporation and seed tuber planting depth on the yield of the potato (Solamum tuberosum L.) cultivars Estima and Maris Piper and the population control of the potato cyst nematodes Globodera rostochiensis Woll. (Skarbilovich) and G. pallida (Stone). The nematicide fosthiazate was applied at 3 kg^?1 ha and either not incorporated, or incorporated to 20 cm or 35 cm. Potatoes were mechanically planted to three depths; approximately 10 cm, 15 cm and 25 cm. Incorporation to 20 cm with tubers planted at a depth of 10 cm or 15 cm, reduced root invasion compared with the other treatments. Incorporating nematicide to 20 cm also gave consistently higher ware yields and better nematode control than the other incorporation methods, which were not significantly different to the control. However, ware yield and nematode multiplication rate were not significantly affected by planting depth.     

宁夏引黄灌区秸秆还田对麦田土壤硝态氮淋失的影响

以宁夏引黄灌区为例,探索秸秆还田条件下冬小麦土壤硝态氮淋失规律。试验设置常规施肥(CK)、常规施肥条件下施用4500kg/hm2(T1,半量还田)和9000 kg/hm2(T2,全量还田)秸秆3个处理。利用树脂芯法吸附10、20、30、60cm和90cm土层的硝态氮流失量。结果表明:硝态氮(纯N)淋失量6.26—12.85 kg/hm2,是冬小麦施用化肥氮量的2.78%—5.71%。与对照CK相比,T1和T2在10cm土层减少0.09%和3.97%;20cm土层减少8.51%和9.81%;30cm土层减少2.25%和10.34%;60cm土层减少23.85%和13.08%;90cm土层减少27.65%和20.73%。10cm和20cm土层,处理与对照以及处理之间均未到显著性差异(P0.05);30cm处理,T1与CK以及T1与T2未达到显著性差异,但T2与CK达到显著性差异表明全量还田效果最好;60cm土层,处理与对照、以及处理之间均达到显著性差异;90cm土层,处理与对照之间达到显著性差异,处理之间未达到显著性差异。硝态氮淋失主要发生在冬小麦返青至灌浆期间,占全生育期淋失量的52.95%—67.79%。T1、T2冬小麦产量增产率分别为10.11%与11.51%。可见,稻秆还田能够减少灌区土壤硝态氮淋失量。     

Fibrous carrot root responses to irrigation and compaction of sandy and organic soils

Field experiments were performed in Southern Finland on fine sand and organic soil in 1990 and 1991 to study carrot roots. Fall ploughed land was loosened by rotary harrowing to a depth of 20 cm or compacted under moist conditions to a depth of 25–30 cm by three passes of adjacent wheel tracks with a tractor weighing 3 Mg, in April were contiguously applied across the plot before seed bed preparation. Sprinkler irrigation (30 mm) was applied to fine sand when moisture in the 0–15 cm range of soil depth was 50% of plant-available water capacity. For root sampling, polyvinyl chloride (PVC) cylinders (30 × 60 cm) were installed in the rows of experimental plots after sowing, and removed at harvest. Six carrot plants were grown in each of in these soil colums in situ in the field.Fine root length and width were quantified by image analysis. Root length density (RLD) per plant was 0.2–1.0 cm cm^-3 in the 0–30 cm range. The fibrous root system of one carrot had total root lengths of 130–150 m in loose fine sand and 180–200 m in compacted fine sand. More roots were observed in irrigated than non-irrigated soils. In the 0–50 cm range of organic soil, 230–250 m of root length were removed from loosened organic soils and 240–300 m from compacted soils. Specific root surface area (surface area divided by dry root weight) of a carrot fibrous root system averaged 1500–2000 cm² g^-1. Root length to weight ratios of 250–350 m g^-1 effectively compare with the ratios of other species.Fibrous root growth was stimulated by soil compaction or irrigation to a depth of 30 cm, in both the fine sand and organic soils, suggesting better soil water supply in compacted than in loosened soils. Soil compaction increased root diameters more in fine sand than it did in organic soil. Most of the root length in loosened soils (fine sand 90%, organic soil 80%) and compacted soils (fine sand 80%, organic soil 75%) was composed of roots with diameters of approximately 0.15 mm. With respect to dry weight, length, surface area and volume of the fibrous root system, all the measurements gave significant resposes to irrigation and soil compaction. Total root volumes in the 0–50 cm of soil were 4.3 cm³ and 9.8 cm³ in loosened fine sand and organic soils, respectively, and 6.7 cm³ and 13.4 cm³ in compacted sand and organic soils, respectively. In fine sand, irrigation increased the volume from 4.8 to 6.3 cm³.     

Growth Promotion of Fluorescent Pseudomonads and Control of Potato Common Scab in Field Soil with Non-antibiotic Actinomycete-biofertilizer

Field studies on the control of potato common scab were done with non-antibiotic Actinomycete biofertilizer, which was manufactured from swine feces with coprophilous actinomycetes and acidified to pH 5.0 with sulfuric acid. The field soil at pH 5.0 was mixed with 0.56 kg of the acidified biofertilizer per subplot (1.0 x 1.2 m) to a depth of the 15 cm. The scab severity, in terms of the percent coverage of the total surface area of potato tubers, was 10.7%, in the control, while the lesions were slight in the biofertilizer subplot, scab severity being only 2.30/0, and the potato production was increased 3 times with the biofertilizer. The viable counts of Streptomyces scabies in the biofertilizer subplot decreased to 1 × 10³ per gram soil from 5 × 10⁵ by 12 weeks, while the inhabitant fluorescent pseudomonads increased to 2.4 × 10⁷ per gram soil from 3 × 10⁴, and the increased fluorescent pseudomonads were antagonistic to the pathogenic strains.     

宁夏平原北部地下水埋深浅地区不同灌木的水分来源

宁夏平原北部引黄灌区地下水埋深浅是该地区土壤盐碱化的主要原因, 种植耐盐植物可以吸收利用地下水, 在降低地下水位的同时可以减少对地面灌溉的依赖。为了分析银川平原北部4种灌木对不同水源的利用特征, 于2010年生长季测定了灌溉前后20年生多枝柽柳(Tamarix ramosissima)、3年生多枝柽柳、3年生宁夏枸杞(Lycium barbarum)和3年生四翅滨藜(Atriplex canescens)木质部水及不同潜在水源稳定氧、氢同位素组成(δ¹⁸O和δD), 应用IsoSource同位素线性混合模型估算了不同灌木对不同水源的利用率。同时测定了0-200 cm土壤剖面的全盐含量、含水量和pH值以及灌溉前后光合气体交换参数。结果表明: 不同深度土壤水δ¹⁸O和δD值存在较大差异, 并呈规律性变化。土壤水δ¹⁸O和δD值随深度加深呈逐渐降低的趋势。灌溉后80 cm以上土壤水δ¹⁸O和δD值低于灌溉前。无论灌溉前还是灌溉后, 20年生多枝柽柳与3年生灌木相比具有更低的δ¹⁸O和δD值。灌溉前, 3年生多枝柽柳、宁夏枸杞和四翅滨藜主要利用表层土壤水(70.1%、52.3%和48.9%); 20年生多枝柽柳对地下水的利用率最高(21.5%)。灌溉后, 3年生多枝柽柳和宁夏枸杞对80-140 cm土壤水利用率较高(59.5%和58.8%)。20年生多枝柽柳对地下水的利用率最高(18.3%)。灌溉前, 20年生多枝柽柳净光合速率、气孔导度和蒸腾速率显著高于其他3种灌木, 灌溉后3年生四翅滨藜净光合速率最高。灌溉对3年生多枝柽柳和宁夏枸杞的净光合速率和气孔导度有显著影响。无论灌溉前还是灌溉后, 3年生四翅滨藜瞬间水分利用效率均高于其他3种灌木。研究表明, 不同灌木在不同水分条件下水分利用策略不同, 这主要与植物种类及树龄有关。灌溉前幼龄多枝柽柳凭借其对干旱较强的忍耐能力利用浅层不饱和土壤水, 灌溉后其又转而利用中层土壤水, 表现出潜水湿生植物的特征, 主要吸收利用深层土壤水分, 对灌溉反应不明显。     

The effects of soil moisture at the time potato tubers are forming on the incidence of common scab (Streptomyces scabies)

Two complementary field experiments at Rothamsted in 1965, with the potato variety Majestic, related the incidence of common scab (Streptomyces scabies) to rainfall, soil moisture and time of tuber formation. In plots where the soil was maintained at field capacity (less than 10 cm. Hg moisture tension) by watering, tubers had little or no scab; infection increased in amount on plots allowed to dry to 30 cm., 50 cm. or more Hg moisture tension during late June. The time tubers formed was varied by planting sprouted (chitted) and non-sprouted seed tubers, and tuber development and scab incidence were observed on sample plants lifted at frequent intervals from unwatered plots. Scab lesions were first seen on 12 July when the distribution of lesions on the surface of tubers was affected by size of tuber both within and between the different seed-tuber treatments. These differences were correlated with estimates of tuber size on 28 June, the beginning of the first dry period. Tubers 1.0 cm. or more in diameter on 28 June had few or no lesions at the stolon attachment (heel) end of tubers on 12 July, whereas tubers smaller than this on 28 June had many lesions in this region on 12 July. The larger the tuber was on 28 June, the greater was the area free from scab lesions on 12 July.     

Effect of Time of Inoculation with Xanthomonas campestris pv. mangiferaeindicae on Mango Fruits Susceptibility Epiphytic Survival of X. c. pv. mangiferaeindicae on Mango Fruits in Relation to Disease Development

Susceptibility of mango fruits to bacterial black spot disease was related to the stage of fruit development and to climatic factors (rainfall and temperature). The highest percentages of infected fruits occurred when inoculations were performed during the month just before harvest. Wounds and lenticels are effective entry sites for the bacterium. The ability of lenticels to take up bacterial inoculum was estimated using safranin. The susceptibility of lenticels to entry of the pathogen was directly related to the fruit age. X. c. pv. mangiferaeindicae can survive epiphytically on immature mango fruits. Bacterial populations around 10⁵ c.f.u./fruit are commonly detected. Epiphytic X. c. pv. mangiferaeindicae were not detected on symptomless mature fruits. Those resident populations are an important source of inoculum for fruit infection. The number of bacterial spots occurring on the fruits is directly related to epiphytic populations.     

Effects of Spilled Oil on Bacterial Communities of Mediterranean Coastal Anoxic Sediments Chronically Subjected to Oil Hydrocarbon Contamination

The effects of spilled oil on sedimentary bacterial communities were examined in situ at 20 m water depth in a Mediterranean coastal area. Sediment collected at an experimental site chronically subjected to hydrocarbon inputs was reworked into PVC cores with or without a massive addition of crude Arabian light oil (∼20 g kg⁻¹ dry weight). Cores were reinserted into the sediment and incubated in situ at the sampling site (20 m water depth) for 135 and 503 days. The massive oil contamination induced significant shifts in the structure of the indigenous bacterial communities as shown by ribosomal intergenic spacer analysis (RISA). The vertical heterogeneity of the bacterial communities within the sediment was more pronounced in the oiled sediments particularly after 503 days of incubation. Response to oil of the deeper depth communities (8–10 cm) was slower than that of superficial depth communities (0–1 and 2–4 cm). Analysis of the oil composition by gas chromatography revealed a typical microbial alteration of n-alkanes during the experiment. Predominant RISA bands in oiled sediments were affiliated to hydrocarbonoclastic bacteria sequences. In particular, a 395-bp RISA band, which was the dominant band in all the oiled sediments for both incubation times, was closely related to hydrocarbonoclastic sulfate-reducing bacteria (SRB). These bacteria may have contributed to the main fingerprint changes and to the observed biodegradation of n-alkanes. This study provides useful information on bacterial dynamics in anoxic contaminated infralittoral sediments and highlights the need to assess more precisely the contribution of SRB to bioremediation in oil anoxic contaminated areas.     

Vertical distribution in and isolation of bacteria from Lake Vanda: an Antarctic lake

Vertical distribution of bacteria in Lake Vanda, an Antarctic meromictic lake, was examined by the acridine orange epifluorescence direct count method. Total bacteria were 10⁴–10⁵ cells · ml^–1 in the water at 55 m depth and above, and increased drastically to 10⁷ cells · ml^–1 in the bottom water. Filamentous or long rodshaped bacteria occurred at a high frequency in the upper layers, but in the bottom layers most bacteria were coccoidal or short rods. Mean bacterial cell volume in water of between 10 m and 60 m deep was fairly large compared with common bacterial populations in seawater and lake water. Aerobic heterotrophic bacteria were recovered from the water of a depth of 30 m and above, and were assumed to belong to Caulobacter. Viable heterotrophic bacteria were not recovered from the high salinity deep water by media prepared with the same deep water. Phototrophic purple non-sulphur bacteria were isolated by enrichment cultures from water at 55 m depth.     

Water relations, gas exchange characteristics, and the level of some metabolites in two cultivars of spring wheat under different N regimes

Twenty eight-day old plants of two spring wheat cultivars differing in salinity tolerance were subjected to varying levels of nitrogen (56, 112, and 224 mg N·kg⁻¹ soil) for 42 days. Both cultivars performed differently under varying soil N levels in terms of growth, and grain yield and yield components. Nitrogen levels, 112 and 224 mg·kg⁻¹ soil, caused maximal growth in Sarsabz and Barani-83, respectively. Cv Sarsabz maintained higher leaf water and turgor potentials, but lower leaf osmotic potential than those of Barani-83 at all external N regimes. Sarsabz had higher Chl a, Chl b and carotenoids contents in leaves than those in Barani-83 at 56 and 112 mg N·kg⁻¹ soil. Sarsabz had higher contents of leaf soluble proteins, soluble sugars, and free amino acids than those in Barani-83 at all external N levels. In Barani-83 net CO₂ assimilation rate remained almost unchanged, whereas in Sarsabz it decreased consistently with increase in external N level. The better growth performance of Sarsabaz as compared to Barani-83 under varying soil N levels except 224 mg N·kg⁻¹ soil was associated with maintenance of high leaf turgor potential but not with net CO₂ assimilation rate.     

Depth distribution of microbial production and oxidation of methane in northern boreal peatlands

The depth distributions of anaerobic microbial methane production and potential aerobic microbial methane oxidation were assessed at several sites in both Sphagnum- and sedge-dominated boreal peatlands in Sweden, and compared with net methane emissions from the same sites. Production and oxidation of methane were measured in peat slurries, and emissions were measured with the closed-chamber technique. Over all eleven sites sampled, production was, on average, highest 12 cm below the depth of the average water table. On the other hand, highest potential oxidation of methane coincided with the depth of the average water table. The integrated production rate in the 0–60 cm interval ranged between 0.05 and 1.7 g CH4 m ^–2 day^– and was negatively correlated with the depth of the average water table (linear regression: r ² = 0.50, P = 0.015). The depth-integrated potential CH₄-oxidation rate ranged between 3.0 and 22.1 g CH₄ m^–2 day^–1 and was unrelated to the depth of the average water table. A larger fraction of the methane was oxidized at sites with low average water tables; hence, our results show that low net emission rates in these environments are caused not only by lower methane production rates, but also by conditions more favorable for the development of CH₄-oxidizing bacteria in these environments. Correspondence to: I. Sundh.     

Seasonal Migration of Meloidogyne chitwoodi and its Role in Potato Production

Seasonal vertical migration of Meloidogyne chitwoodi through soil and its impact on potato production in Washington and Oregon was studied. Nematode eggs and second-stage juveniles (J2) were placed at various depths (0-180 cm) in tubes filled with soil and buried vertically or in holes dug in potato fields. Tubes were removed at intervals over a 12-month period and soil was bioassayed on tomato roots. Upward migration began in the spring after water had percolated through the tubes. Nematodes were detected in the top 5 cm of tubes within 1-2 months of burial, depending on depth of placement. Potatoes were grown in field plots for 4 or 5 months before the tubers were evaluated for infection. One hundred eggs and J2 per gram soil placed at 60 and 90 cm caused significant tuber damage at the Washington and Oregon sites, respectively. At the Washington site, inoculum placed at 90, 120, and 150 cm caused potato root infection without serious impact on tuber quality, but inoculum diluted 2-8 times and placed at 90 cm did not cause root or tuber infection. Nematode migration was dependent on soil texture; 9 days after placement at the bottoms of tubes, J2 had moved up 55 cm in sandy loam soil (Oregon) but only 15 cm in silt loam (Washington). Thus, the importance of M. chitwoodi which occur deep in a soil profile may depend on soil texture, population density, and length of the growing season.     

Effects of variations in soil water potential,depth of N placement,and cultivar on postanthesis N uptake by wheat

This study was conducted to investigate the influence of soil water potential, depth of N placement, timing, and cultivar on uptake of a small dose of labeled N applied after anthesis by wheat (Triticum aestivum L.) Understanding postanthesis N accumulation should allow better control of grain protein concentration through proper manipulation of inputs. Two hard, red spring-wheat cultivars were planted in early and late fall each yr of a 2-yr field experiment. Less than 1 kg N ha^–1 as K ¹⁵NO₃ was injected into the soil at two depths: shallow (0.05 to 0.08 m) and deep (0.15 to 0.18 m). In both years an irrigation was applied at anthesis, and injections of labeled N were timed 4, 12, and 20 days after anthesis (DAA). Soil water potential was estimated at the time of injection. Mean recovery of ¹⁵N in grain and straw was 57% of the ¹⁵N applied. Recovery did not differ between the high-protein (Yecora Rojo) and the low-protein (Anza or Yolo) cultivars. Mean recovery from deep placement was 60% versus only 54% from shallow placement (p < 0.01). Delaying the time of injection decreased mean recovery significantly from 58% at 4 DAA to 54% at 20 DAA. This decrease was most pronounced in the shallow placement, where soil drying was most severe. Regressions of recovery on soil water potential of individual cultivar x yr x planting x depth treatments were significant only under the driest conditions. Stepwise regression of ¹⁵N recovery on soil water potential and yield parameters using data from all treatments of both years resulted in an equation including soil water potential and N yield, with a multiple correlation coefficient of 0.64. The translocation of ¹⁵N to grain was higher (0.89) than the nitrogen harvest index (0.69), and showed a highly significant increase with increase in DAA. This experiment indicates that the N uptake capacity of wheat remains reasonably constant between 4 and 20 DAA unless soil drying is severe.     

Tomato root distribution, yield and fruit quality under subsurface drip irrigation

Tomato rooting patterns were evaluated in a 2-year field trial where surface drip irrigation (R0) was compared with subsurface drip irrigation at 20 cm (RI) and 40 cm (RII) depths. Pot-transplanted plants of two processing tomato, `Brigade' (C1) and `H3044' (C2), were used. The behaviour of the root system in response to different irrigation treatments was evaluated through minirhizotrons installed between two plants, in proximity of the plant row. Root length intensity (L _a), length of root per unit of minirhizotron surface area (cm cm^–2) was measured at blooming stage and at harvest. For all sampling dates the depth of the drip irrigation tube, the cultivar and the interaction between treatments did not significantly influence L _a. However differences between irrigation treatments were observed as root distribution along the soil profile and a large concentration of roots at the depth of the irrigation tubes was found. For both surface and subsurface drip irrigation and for both cultivars most of the root system was concentrated in the top 40 cm of the soil profile, where root length density ranged between 0.5 and 1.5 cm cm^–3. Commercial yields (t ha^–1) were 87.6 and 114.2 (R0), 107.5 and 128.1 (RI), 105.0 and 124.8 (RII), for 1997 and 1998, respectively. Differences between the 2 years may be attributed to different climatic conditions. In the second year, although no significant differences were found among treatments, slightly higher values were observed with irrigation tubes at 20 cm depth. Fruit quality was not significantly affected by treatments or by the interaction between irrigation tube depth and cultivar.