Yitzchak Gutterman

Strategies of seed dispersal and germination in plants inhabiting deserts

AbstractMassive seed consumption is typical in many deserts. The “escape” or “protection” strategies of seed dispersal are important, as they prevent massive seed consumption.The more extreme the desert, the more unpredictable the low amounts and distribution of the rains as well as the beginning and length of the season or seasons with rains. Seeds, which have the highest resistance to extreme environmental conditions, develop during germination into seedlings, which are the most sensitive. Therefore, germination of parts of the seed population at their respective proper times spreads the risk over time and is thus very important for plant survival, especially in those plants inhabiting the more extreme deserts.Each of the plant species studied was found to have its own survival strategies of seed dispersal and germination. At least two extreme seed-dispersal and germination strategies have been observed: 1) the “escape” seed dispersal and “opportunistic” portioned seed-germination strategies, such as inSchismus arabicas andSpergulariadiandra, and 2) the “cautious” portioned dispersal by rain of the protected seeds, such as inAsteriscus hierochunticus and portioned dispersal and rapid germination strategies such as inBlepharis spp.The fate of future generations, as far as the germinability of seeds of some species is concerned, depends on the influences of maternal and environmental factors when the seeds are still on the mother plant, mostly during the final stage of seed maturation, as inTrigonella arabica. It may even depend on the position of the caryopsis from which the mother plant originated, as inAegilops geniculata. The dry post-maturation conditions and the environmental factors during seed wetting and germination may also affect the percentage of seed germination, as inSchismus arabicus.ГуггерманДля экстремального т ипа пустынь характер на непредсказуемость к оличества и распреде ления осадков, а также начала и продол жительности сезона д ождей. Кроме того, типичным явлением дл я многих пустынь явля ется массовое поедание семян живот ными и насекомыми.Устойчивые к экстрем альным условиям семе на развиваются при прорастании в про ростки, обладающие чр езвычайной чувствительностью. П оэтому для выживания растения в экстремальной пусты не особенно важны вер ные сроки прорастания, а также п рорастание только ча сти семенной популяции. Эти механи змы помогают растени ям снизить риск гибели проростков. Дл я защиты от массового поедания после созревания важны стр атегии “бегства” и “з ащиты” в распространении сем ян.Характерная стратег ия распространения и прорастания семян обнаружена для каждо го изученного вида ра стений. Отмечены два крайних типа стра тегий:1) “бегство” в распрост ранении семян и “оппортунистическа я” стратегия частичног о прорастания семенн ой популяции. Примерами могут служ ить Schismus arabicus и Spergularia diandra, 2) “осторожое” частич ное распространение защищенных семян сем ян при увлажнении, как у Asteriscus pygmaeus, или частичное распр остранение семян в со четании со стратегией быстрого прорастания у видов Blepharis.Свойства семян завис ят от условий во время их развития на материнском растени и, особенно на заверша ющей стадии их созревания, как у Trigonella arabica. У Aegilops geniculata механизм прорастани я семян связан даже с расположением зерновки на материнс ком растении. Свойств а семян и стратегия их прорастания влияю т на развитие растени й последующих поколенийХранение семян после созревания в жарких и сухих условиях, а также усло вия окружающей среды во время увлажнения и прораст ания семян, могут влия ть на процент прорастания семян Schismus arabicus.

Influence of light, temperature, salinity and storage on seed germination of Haloxylon ammodendron

Abstract Haloxylon ammodendron is a shrubby perennial distributed in many sandy and saline areas of deserts of Northwest China. It is an important economic plant used for sand fixation, pasture and fuel. Seed germination is the critical stage for species survival. The optimal temperature for germination is 10°C and germination was the lowest at 30°C in light and darkness. The higher the salinity of NaCl, the lower the percentage of germination, but after exposure to higher salinity, the seed recovery percentage is higher. The seed viability of about 10 months can be extended by cold or ultra dry storage at seed moisture content below 5%.

The germination of mucilaginous seeds of t Plantago coronopus, Reboudia pinnata, and t Carrichtera annua on cyanobacterial soil crust from the Negev Desert

We studied the effect of intact, crushed or sterile cyanobacterial soil crust from the Negev Desert highlands of Israel as substrates for the germination of seeds of three annual plant species from local populations that produce mucilaginous seeds t Plantago coronopus, Reboudia pinnata and t Carrichtera annua. Mucilaginous seeds of these species were wetted on local intact cyanobacterial soil crust which inhibited their germination in comparison with their germination on filter paper. However, the percentage of germination of each species differed on sterile and crushed soil crust after 72 h of wetting. Germination of t Plantago coronopus seeds was inhibited mechanically and biologically on intact soil crust, since it was significantly higher on both crushed and sterile soil crust. Germination of t Reboudia pinnata seeds was slightly mechanically and biologically inhibited on intact soil crust, but germination on live crushed crust was higher than on sterile crushed crust. By contrast, germination of t Carrichtera annua seeds was not mechanically inhibited by live soil crust but there was significant biological acceleration of germination on intact soil crust relative to crushed soil crust. Each of the three species exhibited different requirements for germination. Germination of t P. coronopus is promoted by disturbances and removing the crust components (including its biological and structural effects). t R. pinnata and t C. annua germination is less affected by crust disturbance but is generally inhibited after removing the live components of the cyanobacterial crust.These species differences suggest different functions of the mucilage of the seed coat for the three species.

Genetic resources of wild cereals in Israel and vicinity. I. Phenotypic variation within and between populations of wild wheat, Triticum dicoccoides

SummaryPopulations of wild emmer wheat, Triticum dicoccoides, in Israel, originating from diverse habitats, and tested earlier for allozyme (Nevo et al., 1982) and disease resistance polymorphisms (Moseman et al., 1983a, 1983b; Nevo et al., 1984a, 1984b), were compared and contrasted for performance in agronomically important phenotypic traits. The traits compared involved 10 variables comparing germination, earliness, biomass and yield variables. The field experiments were conducted in 1980, 1981 and 1982 in two relatively standardized and contrasting environments: mesic (Mount Carmel, Haifa) and xeric (Acedat Farm, and Sede Boqer, in the northern Negev desert). The experimental design involved 12 population quadrangles at Avedat Farm in 1980, and rows of randomized genotypes of five populations in both Haifa and Sede Boqer in 1981 and 1982.The results indicate that the characters studied are partly genetically determined. Striking genetic variation was found between and, at least in some characters, also within populations in each site, whereas remarkable environmental variation including genetic-environmental interaction was found between the mesic and the xeric sites. We conclude that natural populations of wild emmer wheat in Israel vary not only in genetic polymorphisms of allozymes and disease resistance, but also in quantitative traits of agronomic importance. These traits are economically significant and should be conserved and utilized in wheat crop improvement.

Genetic resources of wild cereals in Israel and vicinity. II. Phenotypic variation within and between populations of wild barley, Hordeum spontaneum

SummaryPopulations of wild barley, Hordeum spontaneum, in Israel, originating from diverse habitats, and tested earlier for allozyme (Nevo et al., 1979a) and disease resistance polymorphisms (Moseman et al., 1984; Nevo et al., 1984a), were compared and contrasted for performance in agronomically important phenotypic traits. The traits compared involved 10 variables comparing germination, earliness, numerical and weight variables of biomass and yield. The field experiments were conducted in 1980, 1981 and 1982 in two relatively standardized and contrasting environments: mesic (Mount Carmel, Haifa) and xeric Avedat farm, and Sede Boqer (both in the northen Negev desert). The experimental design involved 26 population quadrangles at Avedat farm (1980), and rows of randomized plants of 11 populations in both Haifa and Sede Boqer (1981 and 1982).The results indicate that the characters studied are partly genetically determined. Striking genetic variation was found between and within populations in each site, whereas remarkable environmental variation including genetic environmental interaction was found between the mesic and the xeric sites, as well as between populations and years. We conclude that natural populations of wild barley in Israel vary not only in genetic polymorphisms of allozymes and disease resistance, but also in quantitative traits of agronomie importance. These traits are economically significant and should be conserved and utilized in barley crop improvement.

STRUCTURE AND FUNCTION OF THE MUCILAGINOUS SEED COATS OF PLANTAGO CORONOPUS INHABITING THE NEGEV DESERT OF ISRAEL

ABSTRACT Plantago coronopus var. crassipes is a common annual plant in many areas of the Negev Desert highlands. The dry seed coat cross section and surface structure of P. coronopus seeds before the first wetting were examined by SEM, as were the freeze-dried mucilage and adhesion of the seeds to the soil crust. When wetted, the mucilaginous layer forms, and seeds on the soil surface adhere to the soil crust. Some P. coronopus mucilaginous seeds may be dispersed by rain, even after less then 10 min of wetting. The dry seeds can float on run-on water for 10–44 min and are then dispersed along runnels into depressions, or adhere within a few minutes to the wet soil crust near the dry mother plant. Seeds matured on dry plants in a natural habitat in spring 1995, germinated in December 1995 to 96% after 72 h at 20 °C in light, but only to 2% in dark. The importance of mucilaginous seeds for the survival of the plant species under desert conditions is discussed.

INFLUENCES ON SEED GERMINABILITY: PHENOTYPIC MATERNAL EFFECTS DURING SEED MATURATION

Survival of annual plants, and desert annuals in particular, seems to be dependent on three mechanisms: (1) seed dispersal or topochoric behavior for determining suitable microhabitats; (2) germination at the right time; (3) germination of only part of the seeds at one time, even under optimal conditions (heteroblasty). Environmental factors that determine seed germinability, such as day length and temperature, seed position in the capsule, in the dispersal unit, in the inflorescences and in different inflorescences of the same plant are discussed. These factors affect heteroblasty even during the last days of seed maturation. In plants of different taxa the photoperiodic induction that influences germination is absorbed by the leaves or even by the post-harvested fruit and is transferred to the seeds. Flowers along the same branch produce seeds that differ in their germinability according to the day length during the last few days of their maturation.

The distribution of the phenolic metabolites barbaloin, aloeresin and aloenin as a peripheral defense strategy in the succulent leaf parts of Aloe arborescens.

Aloe arborescens is a large, multi-stemmed shrub. It is used as hedge plants to protect agricultural fields or stock and as horticultural plants in gardens. In natural habitats it is one of the very common Aloe species along the Indian Ocean coast of southern Africa, from the Cape, in the south, to Zimbabwe and Malawi in the north. Secondary phenolic metabolites such as barbaloin (Rf 0.31-0.35), aloeresin (Rf 0.25-0.3) and aloenin (Rf 0.51-0.55) have been found to be distributed in the succulent leaves of Aloe arborescens in a peripheral defense strategy. The youngest leaves have the highest content. The terminal third of each leaf has the highest content and the basal third, the lowest. Along the leaf margins, on the top third and adaxial side, the content is the highest and in the base third, the lowest along the leaf center on the abaxial side. Similar relative amounts of these three secondary phenolic metabolites were found in the different leaf locations. The leaf orientation may affect the total content of these three phenols but not their relative amounts in the different parts of the leaves. It is possible that the more often the plant parts are damaged by consumption by animals such as elephants, kudu or insects, the greater the increase of their phenolic metabolites. This increase may reduce or prevent further consumption when the content of the metabolites reaches a certain level. The plants then have a chance to renew themselves.

Genetic basis of barley caryopsis dormancy and seedling desiccation tolerance at the germination stage.

The genomic regions controlling caryopsis dormancy and seedling desiccation tolerance were identified using 152 F4 lines derived from a cross between Mona, a Swedish cultivar, and an Israeli xeric wild barley Hordeum spontaneum genotype collected at Wadi Qilt, Israel. Dormancy, the inability of a viable seed to germinate, and desiccation tolerance, the ability of the desiccated seedlings to revive after rehydration, were characterized by fitting the germination and revival data with growth curves, using three parameters: minimum, maximum, and slope of germination or revival rate derived by the least square method. The genetic map was constructed with 85 genetic markers (SSRs, AFLPs, STSs, and Dhn genes) using the multipoint-mapping algorithm. Quantitative trait loci (QTLs) mapping was conducted with the multiqtl package. Ten genomic regions were detected that affected the target traits, seven of which affected both dormancy and desiccation tolerance traits. Both the wild barley genotype and the Swedish cultivar contributed the favorite alleles for caryopsis dormancy, whereas seedling desiccation tolerance was attributed to alleles descending from the cultivar. The results indicate that some barley dormancy genes are lost during domestication and that dormancy QTLs are associated with abiotic stress tolerance.

Porcupine diggings as a unique ecological system in a desert environment

SummaryThe influence of porcupine diggings upon annual vegetation on a north-facing hillslope in the Negev Desert, Israel, has been observed for some 10 years. It was found that within the porcupine diggins there are changes over time in terms of species richness, plant density and plant biomass, and that such changes take place in three stages. During the initial growing season (stage 1), species richness, plant density and plant biomass are lower than in the surrounding non-disturbed area, followed by progressive plant succession. Subsequently, a maximum level is attained when a dig becomes 50–60% filled in (stage 2). As the extent of filling exceeds 60%, a decrease in species richness, plant density and plant biomass is observed (stage 3). This process concurs with models derived in other ecosystems with animals that create surface disturbances. The role of porcupine diggings as a model of disturbance and recovery is discussed.