Leaf Epicuticular Wax Content Research Articles

Correlation of Leaf Parameters with Incidence of Papaya Ring Spot Virus in Cultivated Papaya and its Wild Relatives

Papaya ring spot virus (PRSV) disease has been the major impediment in papaya cultivation. The disease is transmitted through three aphid vectors and field tolerance towards this disease varies among Carica papaya cultivars as well as within the Vasconcellea genus. Leaf morphological traits are known to have influence on the probing preferences of aphids. Hence, this study was conducted to know whether the leaf parameters could contribute to the incidence of PRSV possibly by influencing the probing or feeding behaviour of aphid vectors. Leaf parameters viz., leaf thickness, leaf epicuticular wax content, presence and type of trichomes, trichome density were correlated with disease incidence at field conditions. The result revealed that leaf thickness along with epicuticular wax content had significant negative correlation with disease incidence. Similarly, trichome density had negative impact on disease incidence at 99.92% significance level. High epicuticular wax content and high trichome density in V. cauliflora and V. cundinamarcensis were found to be negatively associated with low to very low infection indicating that these parameters may have limited the vector transmission significantly.

Correlation of Leaf Parameters with Incidence of Papaya Ring Spot Virus in Cultivated Papaya and its Wild Relatives

Papaya ring spot virus (PRSV) disease has been the major impediment in papaya cultivation. The disease is transmitted through three aphid vectors and field tolerance towards this disease varies among Carica papaya cultivars as well as within the Vasconcellea genus. Leaf morphological traits are known to have influence on the probing preferences of aphids. Hence, this study was conducted to know whether the leaf parameters could contribute to the incidence of PRSV possibly by influencing the probing or feeding behaviour of aphid vectors. Leaf parameters viz., leaf thickness, leaf epicuticular wax content, presence and type of trichomes, trichome density were correlated with disease incidence at field conditions. The result revealed that leaf thickness along with epicuticular wax content had significant negative correlation with disease incidence. Similarly, trichome density had negative impact on disease incidence at 99.92% significance level. High epicuticular wax content and high trichome density in V. cauliflora and V. cundinamarcensis were found to be negatively associated with low to very low infection indicating that these parameters may have limited the vector transmission significantly.

Leaf epicuticular wax content changes under different rainfall regimes, and its removal affects the leaf chlorophyll content and gas exchanges of Aspidosperma pyrifolium in a seasonally dry tropical forest

Leaf epicuticular waxes are the interface between leaves and the atmosphere, acting in the reduction of water loss. Therefore, we believe this part of the cuticle influences species ecophysiological responses under different rainfall conditions. In this study, we investigated how the leaf epicuticular wax (EW) of Aspidosperma pyrifolium contributes to desiccation reduction, and its impacts on gas exchanges. We selected a site of preserved tropical seasonally dry forest, and analysed both intact leaves (control) and leaves that had the EW removed mechanically (without wax - WW). All measurements were made in May, for two consecutive years, with low (2013) and high (2014) precipitation. The results show that the EW strongly contributes to the maintenance of high photosynthetic rates on leaves, which are able to keep their stomata open for longer periods, with high water use efficiency. WW treatment leaves always presented lower A, gs and WUE rates, even in the wet year, however, most of the physiological losses were observed in the dry year. The WW plants degraded chlorophyll and invested in phenols as a strategy to prevent photo damage caused by the stomatal conductance reduction. Chemically, the major constituents of the EW of A. pyrifolium were triterpene alcohols. Despite the higher EW content in the dry year, the chemical composition was not associated with protection against water loss, since triterpenoids suggest a defence mechanism against herbivory. We concluded that: (i) the EW is important to the maintenance of gas exchanges and leaf metabolism in A. pyrifolium, and (ii) the effects of its removal are more intense in dry years.

Rice root morphological traits are related to isozyme group and adaptation

Rice accessions from the International Rice Research Institute (IRRI) germplasm bank were evaluated for root traits of 40-day-old plants grown in soil in the greenhouse. The 136 accessions represented six groups defined on the basis of isozyme classification, with isozyme group six further subdivided on the basis of origin and morphology. An additional 28 rice cultivars were evaluated for seminal root xylem vessel diameter when grown in pots in a growth chamber. Rice groups differed in root thickness, root xylem vessel diameter, root:shoot ratio, and patterns of root distribution. Isozyme group 1, which corresponds generally to the indica subspecies, had thin, superficial roots with narrow vessels and a low root:shoot ratio. The other major isozyme group, group 6, comprising japonica types, was characterized by thick roots with wider vessels, a greater proportion of the root weight below 15 cm, and a larger root:shoot ratio. On an average, the bulu and temperate group 6 accessions were similar to the non- bulu types except that their root:shoot ratios and proportion of root weight above 15 cm were more similar to group 1. Group 2, with aus types from South Asia, was characterized by intermediate root thickness, but vertical root distribution and root:shoot ratio were more similar to group 6. The minor isozyme groups 3–5 were represented by few accessions, and in general, they had root thickness and root distribution profiles more similar to group 1 than to group 6. While significant differences were observed among isozyme groups for all the traits under study, there was significant variation within groups and groups overlapped for all traits measured. This study highlights the wide range of variability for constitutive root traits in rice. For example, root thickness ranged from 0.68 to 1.04 mm, seminal root xylem vessel diameters from 30 to 58 μm, root:shoot ratios from 0.05 to 0.21, and accessions had from 44 to 73% of the total root weight concentrated in the surface 15 cm of soil. For the 28 cultivars evaluated, root xylem vessel diameter was highly correlated with reported values of leaf epicuticular wax content ( r=0.89). These values indicate the range of genetic variation within the rice genome for root morphological traits.

Evaluating different bahiagrass cytotypes for heat tolerance and leaf epicuticular wax content

Bahiagrass (Paspalum notatum Flugge) is a polymorphic species indigenous to South America which has become naturalized in the southeastern U.S. The most common form in the United States is Pensacola bahiagrass,P. notatum var.saurae Parodi., which is a valuable forage. Pensacola is a sexual diploid, while most other bahiagrasses are apomictic tetraploids. Pensacola bahiagrass is considered to have greater heat tolerance (based on anin vitro heat tolerance test) than a number of otherPaspalum species, but has less leaf epicuticular wax (a drought avoidance mechanism) than other species. Both heat tolerance and leaf epicuticular wax are desirable characteristics for species grown where periodic drought occurs. We measured both characteristics over two years in a collection of 23 bahiagrass accessions, many of which had been collected in South America near the center of origin of the species. The collection included various ploidy levels. For both years, no accessions ranked statistically lower in damage in the heat tolerance test than Pensacola, although eight had significantly higher damage. Two entries in addition to Pensacola had very low damage in the heat tolerance test. Pensacola was high in leaf wax, with 16 accessions rated significantly lower in wax. The accession having the lowest wax content was a triploid, which also exhibited considerable leaf death in the field in response to drought and heat. The diploid entries tended to be higher in leaf wax than the other ploidy levels. This study has identified additional bahiagrass germplasm which may be of use in a breeding program.

Physiological Variation in Tissue Culture Regenerated Apomictic Paspalum dilatatum

Summary Tissue culture techniques provide unique opportunities to introduce variability into vegetatively propagated or apomictic plants. We studied 45 regenerates of apomictic common dallisgrass ( Paspalum dilatatum Poir.) derived via tissue culture to search for variability in characteristics related to stress tolerance. Plants were grown in replicated field nurseries. Characteristics measured were heat tolerance as determined by both the solute leakage and tiller survival methods, leaf epicuticular wax content, and survival under severe water stress. In each test, one or more of the regenerates differed from common dallisgrass. In the solute leakage test, two entries had less damage than common, while seven were damaged more than common. In the tiller survival test, two entries were significantly lower in mortality than common dallisgrass. Three entries had better survival than common in the water stress test, while four entries were significantly higher in mortality. The range in wax values observed in the regenerates was relatively narrow. However, two entries were significantly higher in wax than common, but none were significantly lower. In several cases, some entries differed from common for more than one of the parameters tested, although the majority of the entries did not differ from and probably were similar to common dallisgrass. These findings demonstrate that somaclonal variation expressed in plants regenerated through tissue culture include basic physiological characteristics that influence drought and heat tolerance. Because these changes are in an obligate apomict, they are permanently fixed and will be expressed in subsequent generations.

The Effect of a Drying Top Soil and a Possible Non-hydraulic Root Signal on Wheat Growth and Yield

Research has shown that plants are adversely affected by a drying top soil and that this effect may be caused, at least partly, by a non-hydraulic (hormonal) root signal in response to soil water status and/or soil strength. Most studies done to elucidate root signal effects were limited to the short-term, typically 2 to 3 weeks of plant growth. This study was done to detect a possible non hydraulic root signal in response to a drying top soil and to measure its effect on plant growth and production from emergence to maturity. Wheat (Triticum aestivum L.) plants were established in the growth chamber in soil-filled polyvinyl chloride tubes, 120 cm long and of an internal diameter of 10-2 cm. Soil was well fertilized and wet to field capacity at emergence when three treatments were imposed: (1) tubes were watered from the top as needed to eliminate stress (IR); (2) tubes had a constant water table at a soil depth of 100 to 120 cm, with no applied water (WT); and (3) plants grew on stored soil moisture and were rewatered when water stress developed (SW). Soil moisture profiles, soil strength, shoot water status and different shoot developmental traits as well as yield were measured. The upper part of the soil column in WT became dry and hard while roots reached the water table in less than 30 d. There was no significant difference in midday leaf water potential (LWP) and relative water content (RWC) between IR and WT, while SW plants developed comparatively lower LWP and RWC. WT as compared with IR, resulted in earlier heading, smaller flag leaf area, reduced shoot weight, reduced plant height and greater leaf epicuticular wax content. The earliest effect was seen at 20 d after emergence. Tillers developed after this date had less dry weight in WT than in IR. WT also resulted in smaller biomass but a greater harvest index than IR, so that both treatments had the same grain yield per plant. Since IR and WT treatments did not differ in leaf water status, the effect of WT on the plant was intepreted to result from a non-hydraulic root signal in response to the dry and hard top soil.

Evaluation of Paspalum germplasm for variation in leaf wax and heat tolerance

The genus Paspalum contains a number of important forage grasses, including P. dilatatum Poir. (dallisgrass) and P. notatum Flugge (bahiagrass). Even though many Paspalum species are adapted to moist, humid areas, they frequently are subjected to extended periods of drought stress which reduces forage productivity. This study was initiated to determine the range of variation for different indicators of drought tolerance in several Paspalum species. Fifteen species representing a broad cross section of germplasm were grown in a replicated field nursery and sampled for leaf epicuticular wax content on four dates over three years. Wax was extracted with chloroform and quantified by the dichromate oxidation technique. Heat tolerance (solute leakage technique) was also determined by calculating the ratio of the conductivity of the external bathing solution of leaves following a heat treatment to the conductivity of the bathing solution after leaves were boiled. Wax values of the entries ranged from 5.7 to 0.88 mg/dm2. Both relative rankings and absolute wax values were very consistent across all sampling dates. The accessions of Paspalum nicorae Parodi and P. quandrifarum Lam. were consistently high in wax content, while the accessions of P. commune Lillo and P. unispicatum (Scribn. et Merr.) Nash were consistently low. The heat tolerance testing demonstrated that the accession of P. notatum var. saurae Parodi was the most heat tolerant of the entries. Results from this investigation demonstrate the wide range of diversity that exists for both epicuticular wax and heat tolerance within the genus Paspalum.

A Rapid Colorimetric Method for Epicuticular Wax Contest of Sorghum Leaves1

Epicuticular wax deposition on sorghum [(Sorghum bicolor) L. Moench] leaf blades imparts drought resistance. Screening of a large number of sorghum genotypes for increased leaf epicuticular wax content, utilizing the available gravimetric method, is impractical. A more rapid colorimetric method was developed and evaluated against the current gravimetric method. The colorimetric method is based on the color change produced due to the reaction of wax with acidic K2Cr2O7 reagent. Wax content determined by the colorimetric method was highly correlated (r = 0.984) with that determined by the gravimetric method. Leaf epicuticular wax content in 11 fieldgrown grain sorghum cultivars did not vary between growth stage #4 (tip of flag leaf showing) and #7 (soft dough), at which stages comparable wax readings were obtained among the four top leaf blades. A CK 60 ‘bloomless’ (bmbm) genotype had only half of the epicuticular wax content of the CK 60 ‘normal’ (BmBm) genotype. Ten cultivars, all of the BmBm genotype, significantly differed in epiculticular wax content, ranging from 1.14 to 1.99 (SE = 0.006) mg/dm2 of leaf.