Morphological factors of the central whorl leaf associated with leaf surface wetness and resistance in sorghum to shoot fly,Atherigona soccata*

Earlier studies showed that leaf surface water on the central whorl leaf of sorghum seedlings is associated with resistance to shoot fly. In this study, the results of an experiment to determine if leaf surface wetness (LSW) originates from atmospheric condensation or from the plant are described. Morphological structures: trichomes, stomata, leaf cuticle and quantity of surface wax of the central whorl leaf were also examined for their role in LSW production. The results suggest that LSW of the central whorl leaf originates from the plant and is not due to condensation of atmospheric moisture. The presence of trichomes was indirectly associated with LSW and resistance to shoot fly but stomatal density was not associated with LSW production. The amount of wax extracted per 100 mg of fresh weight varied significantly between genotypes and seedling age. It was more in susceptible than in resistant genotypes; however, cuticular thickness was not associated with resistance. It is suggested that LSW could be the result of some form of cuticular movement of water to the leaf surface.     

Reduction of shoot fly damage in irrigated post-rainy season sorghum by manipulating irrigation

Soil moisture was manipulated in an attempt to control shoot fly (Atherigona soccata Rondani) incidence in irrigated post-rainy season sorghum grown under a rainout shelter (ROS) and in field conditions. After uniform irrigation at sowing, the plants were subjected to water stress at young seedling stage (7–28 days after emergence, DAE) for different lengths of time. Soil water had profound effects on the production of water droplets on the surface of the central whorl leaf of seedlings (leaf surface wetness, LSW) of sorghum genotypes. LSW, which facilitates movement of the larvae, was more drastically affected in susceptible (CSH 5) than in moderately resistant (IS 1054) sorghum genotypes. Shoot fly oviposition (infestation) and deadhearts (crop damage) were much higher in treatments with full irrigation (control) than in treatments to which less water was applied during the first 3 wk after seedling emergence. This resulted in higher plant biomass and overall grain yield in the latter treatments than in the control. Using insecticides to control shoot fly infestation, it was shown that a simple cultural practice of inducing plant stress by reduced soil moisture content during early plant growth gave the same or better control of shoot fly damage and the same or higher grain yield than insecticide-protected plots with full irrigation. Thus the costs associated with irrigation requirement and insecticide can be greatly reduced in the former management option compared with the latter. It is suggested that manipulation of soil water content during the vulnerable early stages of crop growth can reduce shoot fly damage in irrigated post-rainy season sorghum.     

Resistance in sorghum to shoot fly Atherigona soccata: Evidence for the source of leaf surface wetness

Leaf surface wetness (LSW) of the central whorl leaf of sorghum seedlings has been associated with susceptibility to shoot fly. Previous physical and physiological evidence suggested that LSW originates from the plant. This was confirmed by radioactive labelling methods using tritium and carbon-14. Tritiated water applied to the soil of potted seedlings was translocated to the surface of the whorl leaf. There were significant differences in the amount of tritiated water collected from susceptible (CSH 5) and resistant (IS 18551) genotypes. Studies with carbon-14 labelling of sorghum seedlings indicated the presence of (small amounts of) solutes in the surface water that may affect larval movement and survival.     

Resistance in sorghum to the shoot fly, Atherigona soccata: epicuticular wax and wetness of the central whorl leaf of young seedlings

Sorghum genotypes known to be resistant or susceptible to shoot fly, Atherigona soccata Rondani were examined by scanning electron microscopy for differences in epicuticular wax structure and wetness of the central leaf whorl. Two major types of wax structures were observed: shoot fly resistant and moderately resistant genotypes were characterised by a smooth amorphous wax layer and sparse wax crystals while susceptible genotypes possessed a dense meshwork of crystalline epicuticular wax. The density of wax crystals decreased from the third leaf to the seventh leaf stage and was related to both seedling age and leaf position. Water droplets on susceptible genotypes with dense wax crystals showed spreading at the edges indicating a tendency to wet easily. In resistant genotypes with less dense wax crystals the droplets remained intact and did not spread.     

The dynamics of leaf surface wetness of sorghum seedlings in relation to resistance to the shoot fly, Atherigona soccata

In quantitative measurements of leaf surface wetness (LSW) of the central whorl leaf of sorghum seedlings in August (rainy season) and November (post-rainy season), the highest amount (6.29 mg of water) was recorded in August in the shoot fly Atherigona soccata (Diptera: Muscidae), susceptible sorghum genotype CSH 1, while the lowest (0.07 mg) was recorded in November in the resistant genotype IS 18551. Studies on diurnal fluctuation revealed that LSW was lowest at sunset, was highest between 02.00 and 04.00 h (closely corresponding with hatching of shoot fly eggs) and dropped before sunrise. This fluctuation was associated with the evaporation of water from the plant during the night. More LSW accumulation occurred during the main crop season (June-October) than in the post-rainy season (November-April). Annual fluctuation of LSW followed trends similar to the population dynamics of shoot fly and crop infestation and were correlated with rainfall, temperature and relative humidity. Measurements of leaf temperature and the vapour pressure gradient between the leaf and the air indicated that leaf surface water originates from the plant. This was further supported by the different amounts of LSW on susceptible and resistant cultivars with similar microclimatic conditions.     

Morphophysiological and biochemical attributes influence intra-genotypic preference of shoot fly [Atherigona soccata (Rondani)] among sorghum genotypes

Shoot fly [Atherigona soccata (Rondani)] is a destructive pest of sorghum at the seedling stage and causes huge losses to grain yield and green fodder. The host-plant resistance mechanism is the best approach to reduce the attack of insects in plants. The damage parameters, morphophysiological traits, and biochemical metabolites had been investigated in the leaves and stem of contrasting sorghum genotypes, viz., resistant (IS18551, ICSV705, ICSV700), moderately resistant (PSC-4), and susceptible (SWARNA and SL-44) at 15 and 21 days after emergence (DAE) against shoot fly infestation. The resistant genotypes recorded lowest shoot fly oviposition and incidence (0.3–0.7 eggs plant⁻¹ and 10–15%) than the susceptible genotypes (2.4–3.0 eggs plant⁻¹ and 70–80%), respectively. The susceptible genotype SWARNA recorded 50% and 80% higher deadheart formation than the resistant genotype IS18551 at 15 and 21 DAE, respectively. Resistant genotypes exhibited higher trichome density at adaxial and abaxial part of leaf (118–145 and 106–131) with pink colored leaf sheath (scale 1.50–3.25), glossy leaves (scale1.00–1.25), and lower leaf surface wetness (scale1.25–2.00) compared with susceptible genotype with 49.3–73.3 and 25.3–64.0, scale 2.50–4.00, scale 2.75–3.50, and scale 3.25–4.25 for the respective parameters. Another defense response of sorghum toward the insect attack was modulation of plant metabolism. The infested genotypes responded to insect attack by upregulation of total soluble sugar, total phenol, prussic acid, and chlorophyll content by 1.2–2.1-fold, 1.5–2.0-fold, 1.2–1.3-fold, and 1.2–3.9-fold with more induction in susceptible genotypes at 21 DAE. On the whole, the present study indicates that morphophysiological and biochemical attributes contribute toward the resistance mechanism in sorghum against shoot fly infestation.

     

Physico‐chemical mechanisms of resistance to shoot fly,Atherigona soccata in sorghum,Sorghum bicolor

Sorghum shoot fly, Atherigona soccata is an important pest of sorghum, and host plant resistance is one of the important components for minimizing the losses due to this pest. Therefore, we evaluated a diverse array of sorghum genotypes to identify physico‐chemical characteristics conferring resistance to A. soccata. Susceptibility to shoot fly was associated with high amounts of soluble sugars, fats, leaf surface wetness and seedling vigour; while leaf glossiness, plumule and leaf sheath pigmentation, trichome density and high tannin, Mg and Zn showed resistance to shoot fly. Stepwise regression indicated that Mg, Zn, soluble sugars, tannins, fats, leaf glossiness, leaf sheath and plumule pigmentation and trichome density explained 99.8% of the variation in shoot fly damage. Path coefficient analysis suggested that leaf glossiness, trichome density, Mg and fat content and plant plumule pigmentation can be used as markers traits to select for shoot fly resistance in sorghum.     

Leaf surface chemistry of sorghum seedlings influencing expression of resistance to sorghum shoot fly, Atherigona soccata

Sorghum shoot fly, Atherigona soccata is one of the serious constraints to sorghum production, and host plant resistance is an important component for controlling this pest. We studied the expression of resistance to A. soccata in a diverse array of sorghum genotypes in relation to composition of leaf surface chemicals during the seedling stage. The sorghum genotypes IS 1054, IS 1057, IS 2146, IS 4664, IS 2312, IS 2205, SFCR 125, SFCR 151, ICSV 700, and IS 18551 exhibited antixenosis for oviposition, and suffered less deadhearts due to sorghum shoot fly, A. soccata. Compounds undecane 5- methyl, decane 4- methyl, hexane 2, 4- methyl, pentadecane 8- hexyl, and dodecane 2, 6, 11- trimethyl, present on the leaf surface of sorghum seedlings, were associated with susceptibility to shoot fly; while 4, 4- dimethyl cyclooctene was associated with resistance to shoot fly. The compounds associated with resistance/susceptibility to shoot fly, can be used as marker traits to select for resistance as well as for diversifying and increasing the levels of resistance to this pest. The role of biochemical compounds for developing sorghum varieties with resistance to shoot fly, A. soccata has been discussed.     

Genomic diversity among sorghum genotypes with resistance to sorghum shoot fly, Atherigona soccata

Host plant resistance is one of the important components for management of sorghum shoot fly, Atherigona soccata. The levels of resistance in cultivated germplasm are low to moderate, and therefore, it is important to identify sorghum genotypes with diverse mechanisms of resistance based on physico-chemical and or molecular markers. We assessed the genetic diversity of 15 sorghum genotypes with different levels of resistance/susceptibility to shoot fly, A. soccata using 93 sorghum simple sequence repeat (SSR) primer pairs and simultaneously characterized for 15 morpho-biochemical traits associated with shoot fly resistance. Of these 93 SSR primer pairs, amplification products from 79, thought to correspond to single-copy loci distributed across all ten sorghum chromosome pairs, showed good polymorphism across the 15 sorghum genotypes. The polymorphic information content (PIC) values of these 79 SSR markers ranged from 0.06 to 0.86. The Principal Coordinate Analyses (PCoA) and cluster analyses based on dissimilarity matrices derived from SSR based allelic variation (Neighbor-Joining distance) and variation in 15 morpho-biochemical traits (based on Gower??s distance), revealed grouping of most susceptible genotypes in single cluster. The improved breeding lines grouped with resistant or susceptible genotypes, based on shared pedigree. Based on these results, three resistant accessions viz., IS 1054, IS 1057 and IS 4664 were found diverse to IS 18551, which is widely used as shoot fly resistance donor. These diverse sources, after further characterization for resistance mechanisms, can be used in breeding programs for improving shoot fly resistance.     

Occurrence of Inverted Water Potential Gradients between Soil and Bean Roots

Measurements with a pressure chamber were made of the xylem water potential of leaves, shoots and roots from bean plants (Pkaseolus vulgaris L. cv. Processor) grown with a 12 hour dark period and natural or artificial light conditions during the day. The water potentials were measured at the end of a dark period and during the light period. Measurements taken at the end of the dark period indicated normal potential gradients within the soil/plant system (leaf < shoot < root < soil), when the matric potential of soil water was relatively high (above ?0.02 bar), and the gradients then also remained normal during the day (natural light). When the soil water potential was ?1 bar or lower in the morning, however, the root xylem water potential was higher than the soil water potential; at very low soil water potentials (< ?4 bar) it remained higher during most of the day. In this case also leaf and shoot xylem water potentials were higher than the soil water potential in the early morning, although decreasing rapidly in daylight. Under artificial light, both leaf and root water potentials were higher than the soil water potential throughout the whole diurnal cycle when the latter potential was below ?4 bar. From measurements of stomatal diffusion resistance, transpiration, relative water content of leaves and of changes in the matric potential of soil water, it was concluded that when the matric potential of soil water was low, water could be taken up by the plant against a water potential gradient. Because leaf xylem water potential was always lower than root xylem water potential, the mechanism involved in the inversion of water potential gradient must be localized in the roots, and probably related to ion uptake. Symbols and abbreviations used in the text: Ψ: Plant water potential (thermocouple psychrometer); Ψx: Xylem water potential (pressure chamber); Ψs: Osmotic potential of xylem sap; Ψm: Matric potential of soil water; RWC: Relative water content.     

Effects of Leaf Wetness Duration and Inoculum Level on Resistance of Wheat Genotypes to Pyrenophora tritici-repentis

Percent leaf necrosis and lesion length on wheat genotypes increased markedly with increasing duration of leaf wetness (up to 24h or 48 h) following inoculation with Pyrenophora tritici-repentis. A long wetting duration favoured less disease development on resistant (Fink's'), and moderately resistant (Bon/YR/3/F3570//KAL/BB) genotypes than on susceptible Glenlea. No significant difference in per cent necrosis was detected among the upper three leaf positions within a genotype. A long wetness duration had a varying effect on the resistance of wheat genotypes, depending upon the inoculum level. Increasing the inoculum level along with the leaf wetness period increased the per cent leaf necrosis on all three wheat genotypes tested. However, the ranking of the genotype for resistance did not alter even after prolonged duration of leaf wetness (up to 96 h) and/or high inoculum level (12000 conidia/ml water). Various post-inoculation wet-periods in combination with high conidia concentrations in inoculum should be used in identifying highly resistant germplasm in breeding populations at the seedling stage of the wheats.     

Identification and validation of genomic regions that affect shoot fly resistance in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Shoot fly is one of the most important pests affecting the sorghum production. The identification of quantitative trait loci (QTL) affecting shoot fly resistance enables to understand the underlying genetic mechanisms and genetic basis of complex interactions among the component traits. The aim of the present study was to detect QTL for shoot fly resistance and the associated traits using a population of 210 RILs of the cross 27B (susceptible) × IS2122 (resistant). RIL population was phenotyped in eight environments for shoot fly resistance (deadheart percentage), and in three environments for the component traits, such as glossiness, seedling vigor and trichome density. Linkage map was constructed with 149 marker loci comprising 127 genomic-microsatellite, 21 genic-microsatellite and one morphological marker. QTL analysis was performed by using MQM approach. 25 QTL (five each for leaf glossiness and seedling vigor, 10 for deadhearts, two for adaxial trichome density and three for abaxial trichome density) were detected in individual and across environments. The LOD and R ² (%) values of QTL ranged from 2.44 to 24.1 and 4.3 to 44.1%, respectively. For most of the QTLs, the resistant parent, IS2122 contributed alleles for resistance; while at two QTL regions, the susceptible parent 27B also contributed for resistance traits. Three genomic regions affected multiple traits, suggesting the phenomenon of pleiotrophy or tight linkage. Stable QTL were identified for the traits across different environments, and genetic backgrounds by comparing the QTL in the study with previously reported QTL in sorghum. For majority of the QTLs, possible candidate genes were identified. The QTLs identified will enable marker assisted breeding for shoot fly resistance in sorghum.     

Effects of Leaf Wetness Duration and Inoculum Level on Resistance of Wheat Genotypes to Pyrenophora tritici-repentis

Percent leaf necrosis and lesion length on wheat genotypes increased markedly with increasing duration of leaf wetness (up to 24h or 48 h) following inoculation with Pyrenophora tritici-repentis. A long wetting duration favoured less disease development on resistant (Fink's'), and moderately resistant (Bon/YR/3/F3570/KAL/BB) genotypes than on susceptible Glenlea. No significant difference in percent necrosis was detected among the upper three leaf positions within a genotype. A long wetnessduration had a varying effect on the resistance of wheat genotypes, depending upon the inoculum level. Increasing the inoculum level along with the leaf wetness period increased the per cent leaf necrosis on all three wheat genotypes tested. However, the, ranking of the genotype for resistance did not alter even after prolonged duration of leaf wetness (up to 96 h) and/or high inoculum level (12000 conidia/ml water). Various post-inoculation wet-periods in combination with high conidia concentrations in inoculum should be used in identifying highly resistant germplasm in breeding populations at the seedling stage of the wheats.     

The gradient between pre-dawn rhizoplane and bulk soil matric potentials, and its relation to the pre-dawn root and leaf water potentials of four species

Uptake of soil water by plants may result in significant gradients between bulk soil and soil in the vicinity of roots. Few experimental studies of water potential gradients in close proximity to roots, and no studies on the relationship of water potential gradients to the root and leaf water potentials, have been conducted. The occurrence and importance of pre-dawn gradients in the soil and their relation to the pre-dawn root and leaf water potentials were investigated with seedlings of four species. Pre-germinated seeds were grown without watering for 7 and lid in a silt loam soil with initial soil matric potentials of -0.02, -0.1 and -0.22 MPa. Significant gradients, independent of the species, were observed only at pre-dawn soil matric potentials lower than -0.25 MPa; the initial soil matric potentials were -0.1 MPa. At an initial bulk soil matric potential of -0.22 MPa, a steep gradient between bulk and rhizoplane soil was observed after 7 d for maize (Zea mays L. cv. Issa) and sunflower (Helianthus annuus L. cv. Nanus), in contrast to barley (Hordeum vulgare L. cv. Athos) and wheat (Triticum aestivum L. cv. Kolibri). Pre-dawn root water potentials were usually about the same as the bulk soil matric potential and were higher than the rhizoplane soil matric potential. Pre-dawn root and leaf water potentials tended to be much higher than rhizoplane soil matric potentials when the latter were lower than -0.5 MPa. It is concluded that plants tend to become equilibrated overnight with the wetter bulk soil or with wetter zones in the bulk soil. Plants can thus circumvent negative effects of localized steep pre-dawn soil matric potential gradients. This may be of considerable importance for water uptake and growth in drying soil.     

Infestation of cassava genotypes by Neosilba perezi (Romero & Ruppell) (Diptera: Lonchaeidae)

The objectives of this work were to assess the infestation of ten genotypes of cassava by the shoot fly Neosilba perezi (Romero & Ruppell) and to investigate effects of plant age, temperature or precipitation on cassava plants infestation by the shoot fly. Thirty-two individuals of each cassava genotype were planted and analyzed every two weeks in order to calculate the percentage of plants infested by shoot fly larvae at each sampling event and per genotype. Infestation by the fly was different across the genotypes. Genotype IAC Caapora 105-66 and genotype IAC Cascuda were resistant to shoot fly infestation, whereas the genotype IAC 15 was the most susceptible to this insect. Plant age may have an influence on infestation by shoot flies. Advanced plant age apparently favors lower or even inexistent infestation rates. However, infestation rate does not seem to be affected by temperature or precipitation.     

Morphological traits of wheat (Triticum aestivum L.) associated with resistance to shoot fly,Atherigona approximata Malloch

Shoot flies (Atherigona spp.) are the members of muscidae family which have got economic importance as pest of several crops of Gramineae family mostly cereals and millets. One of the most effective management strategies for controlling shoot fly is the use of resistant wheat cultivars carrying specific resistant traits. Among thirty wheat genotypes screened at the University of Agricultural Sciences, Dharwad-Karnataka (India), two advanced germplasms UAS BW-12417 and UAS BW-11110 recorded least oviposition and dead heart due to shoot fly and found to be less preferred by Atherigona approximata Malloch. The morphological traits of different wheat genotypes revealed a significant negative correlation of shoot fly oviposition and dead heart with leaf length, leaf length to breadth ratio, seedling height, average seedling growth rate, seedling vigour, leaf glossiness and trichome density of wheat leaves, which indicated the enhanced shoot fly infestation as decrease in the values of above-mentioned morphological traits. Meanwhile, increase in leaf breadth and leaf area of wheat genotype aggrandised the oviposition and dead heart damage by shoot fly. Under the changing climate where, the minor insect pests attaining major pest status, the present investigation would pave way for breeders to tailor future breeding programmes to evolve shoot fly resistant hybrids with high yielding traits.     

Measurement and effects of gel matric potential and expressibility on production of morphogenic callus by cultured sugarbeet leaf discs

During studies to optimize production of morphogenic callus from cultured leaf discs of sugarbeet (Beta vulgaris L.) large differences were observed associated with the gelling agent employed. Water availability, as determined mainly by gel matric potential, was found to be the dominant factor. A simple method was devised to measure the relative matric potential of different gels. A precisely moistened filter-paper disc was placed on the gel surface, allowed to equilibrate, removed and weighed. The relative gain or loss of water from the paper disc was a measure of the matric potential of the gel and varied with both gel type and concentration. Leaf disc expansion and production of callus-derived embryos and shoots were shown to be directly proportional to gel matric potential. Water availability may also be affected by the ease with which liquid is expressed from gels in response to localized pressure caused by explant expansion and contortion. This property, called gel expressibility, was easily measured with a weight and capillary pipette and shown also to vary with gel type and concentration. Validity of the technique for measuring relative matric potential was verified physiologically by culturing leaf discs on filter-paper overlays to eliminate expressibility differences among gels. Additionally, comparison of leaf disc growth on uncovered gel surfaces versus filter-paper overlays demonstrated the contribution of liquid expression to overall water availability. Expression of liquid by explants on uncovered gel surfaces greatly enhanced the production of morphogenic callus.     

Short-term and long-term effects of plant water deficits on stomatal response to humidity in Corylus avellana L.

Short-term (hours) changes in plant water status were induced in hazel (Corylus avellana L.) by changing the evaporative demand on a major portion of the shoot while maintaining a branch in a constant environment. Stomatal conductance of leaves on the branch was influenced little by these short-term changes in water status even with changes in leaf water potential as great as 8 bars. Long-term (days) changes in plant water status were imposed by soil drying cycles. Stomatal conductance progessively decreased with increases in long-term water stress. Stomata still responded to humidity with long-term water stress but the range of the conductance response decreased. Threshold responses of stomata to leaf water potential were not observed with either short-term or long-term changes in plant water status even when leaves wilted. It is suggested that concurrent measurements of plant water status may not be sufficient for explaining stomatal and other plant responses to drought.     

Proline accumulation and nitrate reductase activity in contrasting sorghum lines during mid-season drought stress

Six lines of sorghum ( Sorghum bicolor L. Moench) with differing drought resistance (IS 22380, ICSV 213, IS 13441 and SPH 263, resistant and IS 12739 and IS 12744, susceptible) were grown under field conditions in the semi-arid tropics and analysed for proline and nitrate reductase activity (NRA; EC 1.6.6.1) during a mid-season drought. The resistant lines accumulated high levels of proline, while the susceptible lines showed no significant proline accumulation. Most of the proline was accumulated after growth of the plants had ceased. In a separate greenhouse experiment, most of the proline was found in the green rather than the fired portions of leaves. The levels returned to that of irrigated controls within 5 days of rewatering. Proline levels increased as leaf water potential and relative water content fell, and there was no apparent difference among the different sorghum lines with change in plant water status. Susceptible lines accumulated less proline than resistant lines as leaf death occurred at higher water potentials. Proline accumulation may, however, contribute to the immediate recovery of plants from drought. Leaf NRA reached high levels at about 35 days after sowing in both the stressed and irrigated plants, after which it declined. The decline in NRA was more pronounced in the stressed than in the irrigated plants and closely followed changes in the growth rate. Upon rewatering, NRA increased several-fold in all the lines and, in contrast to proline accumulation, genotypic differences in NRA were small, both during stress and upon rewatering. The high sensitivity of NRA to mild drought stress was reflected in the rapid decline of activity with small changes in leaf water potential and relative water content. The results are discussed in the light of a possible role for proline during recovery from drought, and the maintenance of NRA during stress and its recovery upon rewatering.     

Response of the water status of soybean to changes in soil water potentials controlled by the water pressure in microporous tubes

Water transport through a microporous tube-soil-plant system was investigated by measuring the response of soil and plant water status to step change reductions in the water pressure within the tubes. Soybeans were germinated and grown in a porous ceramic 'soil' at a porous tube water pressure of -0.5 kpa for 28 d. During this time, the soil matric potential was nearly in equilibrium with tube water pressure. Water pressure in the porous tubes was then reduced to either -1.0, -1.5 or -2.0 kPa. Sap flow rates, leaf conductance and soil, root and leaf water potentials were measured before and after this change. A reduction in porous tube water pressure from -0.5 to -1.0 or -1.5 kPa did not result in any significant change in soil or plant water status. A reduction in porous tube water pressure to -2.0 kPa resulted in significant reductions in sap flow, leaf conductance, and soil, root and leaf water potentials. Hydraulic conductance, calculated as the transpiration rate/delta psi between two points in the water transport pathway, was used to analyse water transport through the tube-soil-plant continuum. At porous tube water pressures of -0.5 to-1.5 kPa soil moisture was readily available and hydraulic conductance of the plant limited water transport. At -2.0 kPa, hydraulic conductance of the bulk soil was the dominant factor in water movement.