Significant Difference In Fruit Set Research Articles

Reproductive biology of Trillium govanianum, an endangered plant species endemic to the Himalaya: implications for conservation

ABSTRACT In this study, we investigated the reproductive biology of Trillium govanianum — a medicinally important endangered plant species endemic to the Himalaya. We specifically aimed to unravel the key floral traits that aid and/or limit the species’ reproduction, including the breeding strategies and modes of pollination. We studied qualitative and quantitative floral traits, and conducted different breeding experiments to understand reproductive biology of this plant species for its conservation and sustainable utilization. Our results show no temporal separation between anther dehiscence and stigma receptivity in the species, though essential organs are spatially separated. The absence of nectar secretion in the flowers and lack of pollenkitt in the pollen wall indicates anemophily is operative in the species; nevertheless, some flies and beetles were observed to occasionally visit the plants. The pollen/ovule ratio indicates a value between facultative-xenogamy to xenogamy. Our pollination experiment results reveal that the species undertakes both self- and cross-pollination. We observed a significant difference in fruit set between the supplemented and open-pollinated controls, indicating that the species might be pollen-limited. Although both self- and cross-pollinations are operating in the species, yet the fruit set was low, which may be due to the inefficient pollination system and meiotic abnormality found in the species. Overall, our results suggest that the reproduction in T. govanianum is limited by some inherent biological traits in combination with environmental conditions. Looking ahead, we highlight how our findings can help in guiding conservation of this endangered species in the Himalaya.

Effect of several deficit irrigation schedules on fruit set and fruit growth of olive trees in the north coast region of Egypt

The Mediterranean basin is characterized by severe water scarcity. In some locations, such the north coast of Egypt, with very arid conditions, olive trees are the only option for growers, and can be grown only in irrigated lands. Water availability in these orchards is very limited, and severe deficit irrigation should be scheduled under conditions of high evaporative demand. The aim of this work was to establish the response of fruit set and fruit growth to deficit irrigation. Three deficit irrigation strategies were compared with growers' irrigation in a 10-year-old, 6.4×4.7 m 'Picual' orchard over two consecutive seasons. All treatments used the same amount of water over the season. One of the treatments adjusted the irrigation season in order to apply around 50% of crop evapotranspiration (ETc) over the whole season (T1). In the other treatments, irrigation was provided only during full bloom and fruit set (T2) or in this period and at the beginning of oil accumulation (only 2 weeks) (T3). Finally, growers irrigated over all the season with the amount of water available (T4). During 2009, fruit set was significantly higher in T2 and T3 than in T1 and T4. Fruit growth was also significantly reduced in T4, but not clearly in the rest of treatments. Yield pattern was similar to fruit set. In the 2010 season, there were no significant differences in fruit set or fruit growth. Yield was significantly reduced in T4 with respect to the rest. Influence of irrigation scheduling is discussed.

Increasing Honey Bee Hive Densities Promotes Pollination and Yield Components of Highbush Blueberry in Western Washington

Yield components including fruit set and berry size in northern highbush blueberry (Vaccinium corymbosum) can be limited in key production regions like western Washington. Climactic conditions influence the activity levels of blueberry’s primary commercial pollinator, honey bee (Apis mellifera). Cool springs with frequent rainfall, which are common during the spring bloom period in western Washington, can reduce honey bee activity, pollination efficiency, and subsequent fruit set and yields. Increasing honey bee hive density may be a simple technique that growers can employ to increase the number of honey bees foraging during periods of good weather, interspersed with the poor weather, and therefore, increase fruit set and related yield components. The objective of this study was to evaluate if increased honey bee hive densities improve pollination and subsequent yield components in western Washington blueberry. Three field sites with mature ‘Duke’ plants were stocked with 10 hives/ha of honey bees (control), and three other field sites (also ‘Duke’) were stocked with 20 hives/ha (high hive density). Honey bee visitation and yield components, including fruit set and berry weight, were measured. Estimated yield, seed number/berry, and fruit firmness were also monitored. There were no significant differences in fruit set regardless of honey bee hive density. However, honey bee visitation and estimated yield increased with increased honey bee hive density. Berry weight and seed number per berry were also increased with increased honey bee hive density, although firmness was unaffected. Results indicate that increasing honey bee hive densities can help blueberry growers improve berry size and overall yields, suggesting this is a practice growers can implement if their production is constrained by insufficient pollination.

Pollen-pistil interaction influence on the fruit set of sweet cherry

Pollination success and final fruit set of sweet cherry depends on self- and cross- (in)compatibility relations among cultivars in orchard. The objective of this study was to determine the compatibility relationships and to select pollenizers for the most important Croatian sweet cherry cultivars, ‘Gomilička’ and ‘Stonska’. Phenological observations, pollen germination, pollen tube growth and fruit set were assessed following self- and cross-pollination treatments in two flowering seasons. In general, we found overlap of flowering periods of all cultivars included in the study, but low synchronization was observed for the full-bloom period among traditional cultivars, particularly ‘Stonska’ (early cultivar) and ‘Tugarka’ (late cultivar). There was a significant difference in fruit set among the type of pollinations and pollen donors. ‘Gomilička’ and ‘Stonska’ are self-incompatible, and cross-pollination is necessary for good fruit set. According to the overlap in flowering time and fertilization level in ‘Gomilička’, cross-pollination with ‘Garnet’, ‘Isabella’ and ‘Starking Hardy Giant’ was more effective than that of the traditionally grown cultivars ‘Stonska’ and ‘Tugarka’, and introduction of these cultivars as pollenizers is a good choice that can provide regular and abundant fruit set. Despite the different S-allele combinations of traditional cultivars, overlap in flowering time with some of the introduced cultivars, and favourable climatic conditions, we found also significant effects of pollen-pistil interactions in the style and ovary on the dynamics of pollen tube growth and final fruit set. Inter-incompatibility reactions between cultivars were not observed.

Peach Fruit Set and Buttoning after Spring Frost

Peach fruit set is affected by cumulative chill and spring frost. A spring frost occurred on 29 Mar. 2015 at the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Byron station after 3 weeks of bloom, reducing fruit set and resulting in many buttons (abnormally small fruit with dead embryos). Fruit set was rated in 2014, 2015, and 2016 and button set rated in 2015 using the same scale (0 = no fruit/button to 9 = 1–2 fruit/button at every node). The overall fruit set rating was substantially different in the 3 years, averaging 5.61 in 2014, 2.61 in 2015, and 6.04 in 2016. Buttons and skin-damaged fruit in 2015 varied among peach genotypes. Comparison of fruit and button set ratings showed that there was no difference between cultivars and selections, but some significant differences in fruit set for four ripening months, among the 3 years, and among the nine chilling classes, respectively. Among the cultivars, the most common button set rating was 0–3. For example, ‘Sunprince’, ‘Loring’, and ‘Carored’ trees had a high button set rating, whereas ‘Flameprince’, ‘Julyprince’, and ‘Contender’ trees were low. As for peach selections, BY04P1690n was among those with the highest button set rating. In the population derived from a cross of button-prone BY04P1690n and button-free BY99P3866w, fruit and button counts from 10 long fruiting shoots ranged from 4 to 53 fruit (21.63 on average) and 2 to 27 buttons (10.39 on average). The peach button rate ranged from 5.36% to 87.10% (30.70% on average). The range, distribution, and percentage of the button counts suggested that, if buttoning was genetically controlled, it appeared quantitative. Further assessment is needed.

Pollinator-mediated mating restriction between sympatric varieties of yellow lady’s slipper orchids (Cypripedium parviflorum Salisb.)

A predominant theme in the study of orchid evolution has been the importance of floral traits contributing to pollinator-mediated isolating barriers (i.e., floral isolation). However, few studies have quantified the contribution of floral isolation in sympatric orchid populations. Cypripedium parviflorum vars. makasin and pubescens are excellent taxa to test the strength of floral isolation because of their recent phylogenetic separation, overlapping flowering phenologies, and sympatric populations that can lack intermediate morphologies. In this paper, we use sympatric populations to (1) test for pre-mating and early-acting post-mating reproductive isolating barriers, (2) quantify genetic differentiation among populations using allozyme loci, and (3) document floral size differences between varieties. Pollen tracking experiments using fluorescent powders revealed minimal inter-varietal pollen movement. Across two sympatric sites, only 4 inter-varietal pollinations were observed among 52 var. makasin pollinations and 40 var. pubescens pollinations. All of these inter-varietal pollinations had var. makasin as the pollen donor. In contrast, artificial crosses within and between the varieties revealed no statistically significant differences in fruit set, seed weight, or embryo morphology. Allozyme data are consistent with restricted inter-varietal gene flow, showing strong allele frequency differences between the varieties across multiple loci. In a clustering analysis, these differences caused the varieties to group taxonomically and not by their geographic location. These data along with statistically significant morphological differences between the varieties strongly suggest the existence of a pollinator-mediated isolating barrier. The possible nature of the isolating barrier is discussed as well as the likelihood of other late acting post-zygotic barriers.

Pollination of the heterostylous Galápagos native, Cordia lutea (Boraginaceae)

The hypothesis of this study was that in the Galapagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination due to greater insect activity at night typical of hot, arid regions. Cordia lutea, a heterostylous member of the Galapagos flora, was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen-ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. There was a significant difference in fruit set between flowers experiencing legitimate cross-pollinations (pin × thrum) and those experiencing all other pollination treatments except facilitated autogamy. There was no significant difference in seed set among any of the treatments, but there was a trend toward greater seed set for flowers experiencing open-pollination, legitimate cross-pollination, and nocturnal pollination. There was no significant difference in fruit set or seed set between flowers experiencing diurnal pollination and nocturnal pollination, although there was a trend toward greater seed set resulting from nocturnal pollination. Carpenter bees were the most effective diurnal pollinators, whereas moths were the most effective nocturnal pollinators. Of the two, moths are more efficient at transporting pollen from plant to plant. Results indicate that an overall low productivity of this species is due to pollen limitation exacerbated by nectar robbing. Cordia lutea exhibits a mixed mating system, producing a relatively low level of fruits through a combination of self- and cross-pollination, facilitated by the relatively few insects that are available.

Nocturnal and diurnal pollination of Clerodendrum molle (Verbenaceae) in the Galápagos Islands

The primary hypothesis of this study was that in the Galapagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination because of the greater insect activity at night typical of hot, arid regions. Clerodendrum molle, a widespread member of the Galapagos flora was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen–ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. Results indicate no significant difference in fruit set. Cross-pollinated flowers showed a significant increase in seed set over all treatments except facilitated autogamy. Nocturnal and diurnal fruit and seed set did not differ significantly. Nocturnal visitors included ants, spiders, hawk moths, and roaches whereas diurnal visitors included carpenter bees and ants. Galapagos members of C. molle exhibit incomplete protandry and set fruit via autonomous autogamy as a result of natural selection in an environment with few faithful pollinators. Overall low fruit and seed set are likely because of a combination of pollen and resource limitation, the latter exacerbated by nectar robbing. Studies of island angiosperms are crucial for complete understanding of the population dynamics of indigenous plants, which can assist conservation officials in protecting these species.

Reproductive isolation and pollination success of rewarding Galearis diantha and non-rewarding Ponerorchis chusua (Orchidaceae)

Increasing evidence challenges the conventional perception that orchids are the most distinct example of floral diversification due to floral or prezygotic isolation. Regarding the relationship between co-flowering plants, rewarding and non-rewarding orchids in particular, few studies have investigated whether non-rewarding plants affect the pollination success of rewarding plants. Here, floral isolation and mutual effects between the rewarding orchid Galearis diantha and the non-rewarding orchid Ponerorchis chusua were investigated. Flowering phenological traits were monitored by noting the opening and wilting dates of the chosen individual plants. The pollinator pool and pollinator behaviour were assessed from field observations. Key morphological traits of the flowers and pollinators were measured directly in the field. Pollinator limitation and interspecific compatibility were evaluated by hand-pollination experiments. Fruit set was surveyed in monospecific and heterospecific plots. The species had overlapping peak flowering periods. Pollinators of both species displayed a certain degree of constancy in visiting each species, but they also visited other flowers before landing on the focal orchids. A substantial difference in spur size between the species resulted in the deposition of pollen on different regions of the body of the shared pollinator. Hand-pollination experiments revealed that fruit set was strongly pollinator-limited in both species. No significant difference in fruit set was found between monospecific plots and heterospecific plots. A combination of mechanical isolation and incomplete ethological isolation eliminates the possibility of pollen transfer between the species. These results do not support either the facilitation or competition hypothesis regarding the effect of nearby rewarding flowers on non-rewarding plants. The absence of a significant effect of non-rewarding P. chusua on rewarding G. diantha can be ascribed to low levels of overlap between the pollinator pools of two species.

THE EFFECT OF STAMINODE REMOVAL ON FEMALE REPRODUCTIVE SUCCESS IN A WYOMING POPULATION OF THE ENDANGERED BLOWOUT PENSTEMON, PENSTEMON HAYDENII (SCROPHULARIACEAE)

We examined the effect of removing the staminode of the rare Blowout penstemon, Penstemon haydenii, on female reproductive success in a south-central Wyoming population. We found no significant difference in fruit set or in seeds per fruit between flowers with and without staminodes. The most frequent flower visitor, the megachilid bee, Osmia brevis, modified its behavior when visiting flowers without staminodes. In intact flowers, O. brevis collected pollen by straddling the staminode and rubbing its head and thorax across the anthers. In flowers without staminodes, O. brevis, appeared to compensate for the increased distance to the anthers from the corolla floor by simply stretching its legs to make contact with the anthers. The smaller, native generalist sweat bee (Dialictus pruinosus), which commonly collected pollen in intact flowers, appeared disoriented in flowers without staminodes, and frequently left without collecting pollen. Other taxa (e.g., bumblebees, Bombus spp., the masarid wasp Pseudomasaris vespoides), appeared unaffected and plied the flowers without incident. We speculate that the staminode of Blowout penstemon is intermittently vestigial: where O. brevis, bumblebees, and P. vespoides are common, the staminode is of little consequence; where D. pruinosus is the primary pollinator, the staminode is essential to sexual reproduction by the plant.

Self‐Pollination by Sliding Pollen inCaulokaempferia coenobialis(Zingiberaceae)

Caulokaempferia coenobialis (Zingiberaceae) forms dense populations on steep cliffs in shady, humid monsoon forests in south China. It produces few consecutively opening bright yellow flowers that are 3 cm long and oriented parallel to the ground. Upon anther dehiscence at about 0600 hours, each pollen sac releases a drop of pollen onto the horizontally oriented style, and the two drops then merge to form an oily film that slowly flows toward the stigma, carrying out self‐pollination between about 1500 and 0730 hours the next day. The distance covered by the pollen film is ca. 3 mm. There is no significant difference in fruit set between experimentally cross‐ and self‐pollinated flowers or between naturally pollinated and bagged flowers. The low pollen/ovule ratio of $$6\pm 4$$ probably relates to the pollen grains being held together by pollen‐connecting threads. The latter ensure that pollen grains always arrive as multiples, and this is the first report of such threads in the Zingiberaceae. During 35 h of observation at several locations and during three flowering periods, only three individual bees, five flies, and two butterflies visited single flowers. It remained unclear whether they affected pollination because no return visits were observed. The automatic selfing by pollen that reaches the stigma ca. 9 h after the onset of anthesis apparently constitutes a case of delayed selfing, providing reproductive reassurance in situations of low pollinator visitation.

Mating system and pollination biology of the spring‐flowering shrub, Dirca palustris

Abstract Dirca palustris L., eastern leatherwood or wicopy (Thymelaeaceae), a widely distributed shrub of eastern North America, flowers in early spring and so may face some of the same constraints faced by ephemeral vernal herbs of the eastern deciduous forest, most notably the influence of low temperature on pollinator activity. I studied the mating system of D. palustris and the influence of temperature on pollinator visitation of flowers, during three field seasons in a small stream valley in north‐western Pennsylvania, USA. Specifically, I was interested in how a species with apparently specialized floral morphology, like D. palustris, may ensure reproductive success in a thermally unpredictable vernal environment. Pollinator visitation of flowers of D. palustris was strongly regulated by temperature, with no visits occurring below 14.9°C. Lack of treatment effects in mating system studies, especially the lack of significant differences in fruit set between the bagged, self‐pollination treatment and various cross‐pollination treatments accessible to pollinators, suggests that D. palustris is self‐compatible or perhaps apomictic. Thus, like other spring‐flowering species faced with pollinator unpredictability, D. palustris may rely on a mixed mating system to ensure reproductive success during cool temperate springs.

Behavior and pollination efficiency of Nannotrigona perilampoides (Hymenoptera: Meliponini) on greenhouse tomatoes (Lycopersicon esculentum) in subtropical México.

The acclimation, foraging behavior, and pollination efficiency of stingless bees of the species Nannotrigona perilampoides Cresson were evaluated in tomato (Lycopersicon esculentum Mill.) plants cultivated in two greenhouses. The greenhouses were divided into three areas of 16 m2, and one of the following treatments was used for pollination: stingless bees (SB), mechanical vibration (MV), and no pollination (NP). Observations were conducted once a week from 0800 to 1600 hours during 2 mo. The acclimation of the bees to the greenhouses was estimated by the number of bees that did not return to the hive (lost bees) and by comparing the population of the colonies (brood and adults). The foraging activity of the bees across the day was evaluated by comparing the number of foragers per hour. The influence of environmental variables on the foraging activity was also analyzed. The pollination efficiency was compared among treatments through the percentage of fruit set, weight of individual fruit, kilograms of fruit produced per square meter, and the number of seed per fruit. The bees started foraging on the flowers approximately 7 d after the colonies were introduced to the greenhouse. There was a decline in the population of the colonies across the experiment, but colonies did not die out. Correlations of environmental variables with the foraging activity of the bees showed that none of them had a significant influence on pollen foraging. However, water collection was positively correlated with the temperature and negatively correlated with the humidity inside the greenhouse. The estimation of the pollination efficiency per treatment showed that there were significant differences in fruit set in SB (83 +/- 4.2) and MV (78.5 +/- 6.4) compared with NP (52.6 +/- 7.6). However, the average weight of the fruit was similar for the three treatments (65 g). There were significant differences for seed number in SB (200 +/- 15.3) and MV (232 +/- 21.4) compared with NP (120 +/- 16.6). The productivity in kilograms of fruit per square meter was higher in SB (5.72 +/- 0.61) and MV (5.66 +/- 0.58 kg) compared with NP (3.34 +/- 0.72). The number of seed was positively correlated with the weight of the fruit. We conclude that the use of Nannotrigona testaceicornis Rondani, for pollinating greenhouse tomatoes in tropical climates, could be an alternative to the use of highly defensive African-derived Apis mellifera or non-native bumble bees (Bombus spp.). However, more research is needed to evaluate the cost/benefit on large-scale greenhouse pollination using N. perilampoides Cresson against other bee species and pollination methods.

Effects of auxin application on fruit formation in tomato growing under stress temperatures in the field

SummaryTomato (Lycopersicon esculentum L. Mill) cultivars Early Urbana and Red Clode were grown in the field at adverse temperatures (stress regimes) until they set fruit in two growing seasons (Autumn and Spring) during 1999 and 2000 in Ahwaz (Southern Iran). To test the effectiveness of auxins in enhancing fruit set, racemes of tomato were sprayed during early fruit set with 25, 50 and 100 mg l–1 4-chlorophenoxy acetic acid (4-CPA) and indole-3-butyric acid (IBA) followed by two additional applications at three intervals. The control plants were treated with deionized water. At harvest, racemes from autumn and spring plantings that were treated with 4-CPA had more large fruits than the control racemes. In both growing seasons, neither cultivar showed a significant difference in fruit set in plants treated with IBA, compared with controls. The ratio of fruit/flower in all racemes treated with 4-CPA increased significantly compared with the other treatments. However, auxin treatments did not significantly affect the number of flowers per raceme. Plants treated with 4-CPA produced the highest yield of marketable fruit. The greatest increase in total yield and parthenocarpic fruit occurred with 4-CPA treatments. Also, there was little difference between concentrations of 4-CPA on fruit set in both cultivars. It may be concluded that the response of fruit setting in tomato to either low or high temperatures regimes was auxin dependent and that 4-CPA was more effective than IBA.

Insect flower visitors, foraging behaviour and their effectiveness as pollinators of Persoonia virgata R. Br. (Proteaceae)

Abstract Leioproctus species are frequent flower visitors to Proteaceae and have been inferred as pollinators of many species of Persoonia. This study investigated frequency of flower visitors, their behaviour and the breeding system of Persoonia virgata. The two most frequent visitors were the native bees Trigona carbonaria Smith (Hymenoptera: Apidae) and females of Leioproctus (Cladocerapis) speculiferus Cockerell (Hymenoptera: Colletidae). These species have different foraging strategies on the flowers of P. virgata and, on the basis of more frequent stigma contact, L. speculiferus was found to be the most effective pollinator. Pollination studies indicated that fruit set of bagged flowers (0.5% and 9.2%) was significantly less (P < 0.001) than fruit set of control flowers left open to visitors (24.0% and 48.9%) in two experiments, respectively. Furthermore, flowers that were bagged and cross‐pollinated set significantly (P < 0.001) more fruit (43.8%) than flowers that were bagged and self‐pollinated (6.6%), suggesting partial self‐incompatibility. No significant difference in fruit set was found between control flowers and cross‐pollinated flowers, indicating that flower visitors of P. virgata were efficient vectors of cross‐pollen from plant to plant.

The breeding system of Fumana ericifolia: first evidence of autogamy in woody Cistaceae

Fumana ericifolia belongs to the family Cistaceae, in which all perennial species previously studied have been reported to be self‐incompatible and xenogamous. Here we show that F. ericifolia is self‐compatible and autogamous. Its flowers last only four to eight hours and produce a small amount of pollen and ovules. Self‐pollination depends on changes in the relative position of the stigma and the anthers, triggered by the abscission of the petals; this in turn causes closing of the sepals, which push the anthers onto the stigma. Pollen remains highly viable and germinable, and the stigma keeps its receptivity several hours after the loss of the petals. Hand pollination treatments revealed that fruits are produced both in selfed and crossed flowers. The germination of pollen grains on the stigma, the rate of pollen tube growth along the style, and the penetration into the ovules were similar in self‐and cross‐pollinations; also, there were no significant differences in fruit set, seed set and weight of seeds. Thus, we report the first evidence of autogamy in a woody Cistaceae and suggest that selfing may ensure reproductive success when pollinators are limited.

FUNCTIONAL DIOECY IN ECHINOCEREUS COCCINEUS (CACTACEAE): BREEDING SYSTEM, SEX RATIOS, AND GEOGRAPHIC RANGE OF FLORAL DIMORPHISM

The breeding system of the hedgehog cactus, Echinocereus coccineus Engelm. (Cactaceae), was studied at two sites in the northern Chihuahuan Desert, New Mexico. Two distinct flower types, restricted to separate plants, were observed. One was hermaphroditic and the other male‐sterile. Hand‐pollinations and field observations showed them to be functionally male and functionally female, respectively. There were significant quantitative intersexual differences in floral morphology. The main pollinators of the populations studied are probably two species of halictid bee. Sex ratios based on the number of plants and flowers at the two sites did not differ significantly from 1:1. Significant differences in fruit set existed between functional female plants from the two sites. The floral dimorphism described here appears confined to eastern and northwestern populations, at the periphery of the range of E. coccineus. Floral dimorphism was not observed in three closely related species.

The effect of high temperature regimes or short periods of water stress on development of small fruiting saltana vines

Poor fruit set of sultanas in the Murray Valley is sometimes attributed to excessively high temperatures around flowering time. Experiments with small fruiting sultana vines in pots suggest that water stress is the more important factor. Fruit set was significantly less when a 3-day period of water stress was imposed at flowering or 1, 2, or 4 weeks after flowering, but not when it was imposed 6 weeks after flowering. Three days with maximum temperatures above 45°C at or 1 week after flowering did not reduce fruit set when ample water was supplied. When controlled environments combining day temperatures between 21 and 30°C with night temperatures between 19 and 25° were used, no significant differences in fruit set were found, although shoot growth increased with increasing night temperature. Shoot elongation slowed down during periods of applied water stress but recovered, when the stress was ended, to a rate greater than that of plants which had not been stressed.