Trichome Morphology as an Indicator of High Rubber Bearing Guayule (Parthenium Argentatum Gray) Plants in Native Populations

Abstract

Parthenium argentatum Gray (guayule) and P. incanum (mariola) grow in close associations in their native habitat of Mexico. Variation in rubber concentration and morphology of guayule has been known for a long time. Studies of over 75 native guayule plants indicated the presence of at least three prominent forms of guayule plants. Group I guayule plants have oblanceolate leaves and leaf margins are entire to two‐toothed. T‐shaped leaf trichomes are with centrally attached stalk and cap cell with two blunt ends. Plants in this group are high in rubber, containing on the average 17% rubber. Group II guayule plants have narrow elliptic leaves and leaf margins are entire to four‐toothed. T‐shaped trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and straight. Rubber content in these plants averages 10%. Group III guayule plants have ovate leaves and leaf margins are four‐ to eight‐toothed. T‐trichomes have an acentrally attached stalk and a cap cell with short end blunt, long end pointed and wavy or curved. These plants on the average contain 6% rubber. Morphological as well as biochemical data indicate the presence of mariola genes in the last two groups of plants and this has resulted in an increase in trichome length and a decrease in the rubber content. Group II guayule plants are of more common occurrence than the others. Based on the data presented here, high rubber bearing guayule plants in native stands can be easily selected by analyzing trichome morphology.

Comparative macro- and micro-morphological studies on varieties ofParthenium argentatum Gray (guayule)

“…Nonetheless, the ratio of blunt arms to pointed arms was never significantly correlated with rubber content (Table 4). This is in contrast to the conclusions of Mehta et aL (1979), who found a positive correlation between arm ratio and rubber content in the native guayule population, with arm ratio decreasing as rubber content increased.…”

“…Our results contradict those of Mehta et al (1979), who reported that these characteristics could serve as indicators of the level of rubber production in guayule. Mehta et aL (1979) had reported that these characteristics could be modified by changes in climate, soil properties, or genetic makeup of the plant (Mehta et at., 1979). In the current study, only a limited number of plants (10 to 15 per variety) were available for study.…”

“…However, among these varieties, no consistent decrease or increase was found in cap cell dimensions (Table 1 ). Based on these results of varieties growing in India, therefore, we cannot substantiate the conclusions of Mehta et al (1979), who suggested that cap-cell length decreased with an increase in rubber content.…”

“…These oneyear-old plants had been recently introduced to India through the NBRI, Lucknow. We can only presume that the plants sampled here, possessed the mix of morphological characteristics described by Mehta et al (1979) for three groups of plants.…”

“…Although its variations in leaf form, branching of the inflorescence axis, and other morphological characteristics have been studied extensively (Mehta et al, 1979;Wain et al, 1983;Healey et al, 1986), only. Mehta et al (1979) has attempted to compare a group of such morphological characters (e.g., leaf shape, trichomes) in guayule, with those found in rubber-bearing plants growing in the Mexican desert. Morphological studies enable researchers to determine rubber content without sacrificing the entire plant.…”