Predispersal seed predation on five Piper species in tropical rainforest

Absolute number of seeds lost to predispersal seed predators and proportion of total seeds lost per infructescence were compared among five Costa Rican Piper species of different annual fecundities. Mean seed number and mean seed size in the five species were negatively correlated. The impact of predation on these species was inversely related to the number of seeds they produced. The two early successional species had very high fecundities, a combination of many seeds per infructescence, many infructescences per plant, and, in one species, year-round reproduction. Although seed predators destroyed as many or more seeds of these early successional species than they did of the less fecund, late successional species, this loss accounted for a relatively minor proportion (9 and 12%) of the seeds of the early successional species. In contrast, late successional species produced fewer, larger seeds in a smaller number of infructescences and were not continually in fruit. One of these species, which produced intermediate numbers of intermediately sized seeds, lost 30% of the seeds in each infructescence on average. Seed predators destroyed a larger proportion (65 and 76%) of the seeds per infructescence in the two species with fewest seeds per infructescence. High levels of insect damage in these late successional species caused many of their infructescences to abort prematurely. Taken together these factors resulted in annual fecundities several orders of magnitude smaller in shade-tolerant Piper species than the annual fecundities of shade-intolerant, early successional species. Seedlings of the two early successional species were common in large gaps and other sunny clearings and seedlings of the species with 30% seed loss were occasional, whereas no seedlings were seen of the two species with the highest proportional seed loss, suggesting that seed predation on the latter species may limit seedling recruitment.     

Changes in Baboon Feeding Behavior: Maturity-dependent Fruit and Seed Size Selection within a Food Plant Species

Despite considerable inter- and intraindividual variation in fruit and seed size in many plant species, researchers have given little attention to the relevance of the traits for primate fruit choice within a food plant species and its implications for tree regeneration. We studied feeding behavior and selectivity of olive baboons (Papio anubis) in the African locust bean (Parkia biglobosa, Mimosaceae), via direct observations of habituated groups and indirect evidence from leftovers of pods after feeding events. Olive baboons acted as both seed predators and dispersers for Parkia biglobosa. They fed on and destroyed unripe seeds, and swallowed intact ripe seeds when consuming mature fruit pulp. Predation rate was high, and only 10% of the seeds were dispersed. Predation and dispersal of seeds is linked to seed number and size. Digestible unripe seeds accounted for 10% of the unripe fruit mass, while indigestible ripe seeds made up 28% of the mature fruit mass. With these constraints, olive baboons increased food gain per fruit by selecting unripe pods containing a high number of large and heavy seeds. Consequently, only pods with fewer and smaller seeds remained for maturation. Thereafter, baboons fed on mature pods containing the smallest seeds, and exploited pods with more seeds to a greater extent than those with fewer seeds. Thus, fruits with small seeds and an intermediate seed number contributed the most to dispersal by baboons.     

Patterns of fruit and seed production inBauhinia ungulata (Leguminosae)

Patterns of seed and fruit production ofBauhinia ungulata, a small tree legume indigenous in tropical America, were studied in Costa Rica. Only about 8% of flowers produced fruits. The average pod had 19 ovules and about two thirds of these began seed development, with mature pods containing an average of 9.7 mature undamaged seeds. About half of the mature pods were damaged by herbivores and within these, 27% of ovules or seeds had been eaten. Among trees there was no significant variation in pod production, but the number of ovules per pod and seed production per pod varied significantly. Within infructescences most pods were retained at middle positions. Within pods, the probability of an ovule developing into a seed increased toward the distal end. The pattern of seed and fruit production in this species agrees well in general with that reported for other neotropical legumes. The abortion of seeds and fruits can be regarded as a way of controlling maternal investment, and as a response to herbivory.     

小叶桦花序生长物候及其生态适应意义

小叶桦(Betula microphylla)是一种典型的荒漠和山地乔木植物,在中国仅分布于新疆。为了明确小叶桦花序生长物候规律及发育特征,该研究对小叶桦进行了花序物候观测,分析其生长规律及果实结籽情况。结果显示:小叶桦雄花序为越年生殖器官,物候周期为345d,其中营养生长期154d、休眠期158d、开花生长期33d;雌花序与果序为当年生殖器官,物候期为105d,其中雌花序生长期24d、果序生长期90d。虽然雄花序比雌花序的生长周期明显较长,但开花授粉均在4月中下旬,雄花序散粉期和雌花序可授粉期之间具有较高的同步性和协调性,表现出集中开花授粉模式,同时这种开花模式在自然条件下,果序的结籽数和结籽率分别为220和76.7%,种子库中具有活力的种子约每平米4万粒,表明小叶桦在荒漠极端环境中能顺利完成有性生殖过程。     

Effect ofAspergillus parasiticus soil inoculum on invasion of peanut seeds

Environmental control plots adjusted to late season drought and elevated soil temperatures where inoculated at peanut planting with low and high levels of conidia, sclerotia, and mycelium from a brown conidial mutant ofAspergillus parasiticus. Percentage infection of peanut seeds from undamaged pods was greatest for the subplot containing the high sclerotial inoculum (15/cm² soil surface). Sclerotia did not germinate sporogenically and may have invaded seeds through mycelium. In contrast, the mycelial inoculum (colonized peanut seed particles) released large numbers of conidia into soil. Soil conidial populations of brownA. parasiticus from treatments with conidia and mycelium were positively correlated with the incidence of seed infection in undamaged pods. The ratio ofA. flavus to wild-typeA. parasiticus in soil shifted from 7:3 to 1:1 in the uninoculated subplot after instigation of drought, whereas in all subplots treated with brownA. parasiticus, the ratio of the two species became approximately 8:2. Despite high levels of brownA. parasiticus populations in soil, nativeA. flavus often dominated peanut seeds, suggesting that it is a more aggressive species. Sclerotia of wild-typeA. parasiticus formed infrequently on preharvest peanut seeds from insect-damaged pods.     

Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

Factors affecting intrafruit pattern of ovule abortion and seed production in Hormathophylla spinosa (Cruciferae)

We investigated the pattern of intrafruit seed production in Hormathophylla spinosa (Cruciferae) over a 7-yr period. H. spinosa fruit have two chambers, each chamber containing two ovules, and usually situate perpendicular to the infructescence axis with one chamber above the other. The percentage of ovules ripening to seeds is usually lower than 50%. In addition, we found a consistent position-dependence in seed ripening probability, since more than 90% of the ripe seeds are arranged in the lower chamber of the fruit. This pattern of seed production is not produced by the direct or indirect effect of seed predators, by pollen limitation or by nonrandom fertilizations. By contrast, fruit removal experiments showed that sibling rivalry can partially explain the seed production pattern, be the cause of the reduction in the seed number from the uppermost threshold of 50%. Moreover, experimental manipulations of fruit orientation suggest that the position-dependence in seed production is the cause but not the effect of seed ripening. We presume that some architectural effect is producing a significant increase in the ripening probability of the ovules arranged in the lower chamber, causing thus the observed pattern in the intrafruit seed production in H. spinosa and severely constraining the maximum number of seeds per fruit to two.     

The Effects of Primates and Squirrels on Seed Survival of a Canopy Tree,Afzelia quanzensis,in Arabuko‐Sokoke Forest,Kenya1

I examined the fate of seeds from ten focal trees of Afzelia quanzensis (Leguminosae), a canopy tree in the Arabuko‐Sokoke, Kenya. The study was conducted for one fruiting season, between August 1990 and July 1991. Yellow baboons (Papio cynocephalus), Syke's monkeys (Cercopithecus albogularis), sun squirrels (Heliosciurus rufobrachium), and bush squirrels (Paraxerus palliatus) were all observed to interact with A. quanzensis seeds at various stages of pod development. Baboons and squirrels consumed high percentages of seeds when they were still immature, but the seeds were still unavailable to Syke's monkeys at this stage. Baboons bit open the hard green pods and squirrels gnawed through the pods to extract the immature seeds (hereafter referred to as seed predation), but monkeys were unable to open the pods. Upon maturity, the pods opened slightly, revealing red arils that were sought by baboons, monkeys, and squirrels. Monkeys removed the highest percentage of mature seeds from these pods. These mammal dispersers ate the arils from the mature seeds and discarded the viable part that germinates (hereafter referred to as seed dispersal). My data indicate that baboons and squirrels are seed predators while monkeys are seed dispersers of A. quanzensis.     

Intensity of pre‐dispersal seed predation in the invasive legume Leucaena leucocephala is limited by the duration of pod retention

Abstract The intensity of seed predation the invasive tropical legume Leucaena leucocephala by the bruchid Acanthoscelides macropthalmus was investigated in south‐eastern Queensland, Australia. The number of seeds damaged by A. macropthalmus as a proportion of total seeds available was found to increase the longer the pods remained on the tree. Seed predation ranged from a mean of 10.75% of seeds on pods that remained on the plant for 1 month and increased to 53.54% for pods that remained of the plant for 4 months. The low bruchid populations at high pod densities results in ‘predator satiation’. However, pods dehisce over time and the proportion of pods available over time to the bruchid correspondingly declines. By the time bruchid densities build up, most pods have dehisced and the seeds consequently escape predation. As a result the number of seeds lost to bruchid damage increases only marginally over time. Despite the levels of seed predation observed over the course of the study, the number of seeds in the soil seedbank almost doubled over time increasing from 8.5 seeds m^?3 to 15.5 seeds m^?3 over a 4‐month period. Levels of seed predation and addition of seeds to the soil seedbank were not correlated. The taxonomic (subspecies) status and apparency of host plants as measured by plant and patch traits (average plant height, density of podding plants and patch size) did not influence levels of seed predation. Pre‐dispersal seed predation studies need to take into account the pod/seed retention behaviour of the plant. The ability of the bruchid to regulate the invasiveness of Leucaena through influencing its demography is likely to be diminished if the insect populations cannot increase rapidly enough to use the seeds before pod dehiscence.     

Interactive effect of cytokinin and potassium on sink-source relationships in Lupinus angustifolius

This study examined whether increased K supply in conjunction with BAPcould increase lupin seed yield and harvest index by enlarging sink volume (podnumber), increasing assimilate and improving assimilate partitioning to filltheadditional pods induced by BAP treatment. Narrow-leafed lupin(Lupinusangustifolius, cv. Danja abs^– mutant) was grown inaglasshouse, in pots containing sandy soil with four K treatments (0, 15, 60 and120 mg K/kg soil). BAP (2 mM) was applied daily toallmain stem flowers throughout the life of each flower from opening to senesced.BAP application did not affect assimilate production (as measured by totalabove-ground biomass), but changed assimilate partitioning. On BAP-treatedplants, there were greater proportions of seed to pod wall dry weight on themain stem but smaller proportions on the branches, and an increased weightratioof seed to pod wall overall which meant more assimilate was used for seedgrowthrather than pod wall growth. BAP increased the number of pods per plant by35% and this more than compensated for the decreases in seeds per podandseed weight. Therefore, there was an increased harvest index (+11%)and seed yield per plant (+13%) in BAP-treated plants. BAP alsoincreased the number of pods with filled seeds (146%) on the main stemand main stem seed K⁺ concentration (from 0.81% to0.87%). Added K increased biomass but only slightly affected assimilatepartitioning. As applied K increased, relatively more assimilate was used forpod wall growth rather than seed growth. Added K increased seed yield per plantby about 14% due to increases in seed weight and the number of pods onthe main stem. Moreover, K⁺ concentration in seeds and shootsincreased with increasing level of applied K. Seed yield was enhanced more byBAP when K was supplied at high levels. Increasing K supply interactedpositively with added BAP by increasing narrow-leaf lupin seed yield andharvestindex through increases in assimilate supply and its partitioning into seeds.     

Pod photosynthesis and seed dark CO2 fixation support oil synthesis in developingBrassica seeds

Rate of photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were determined in pods (siliqua), whereas rate of dark CO₂ fixation, oil content and activities of enzymes involved in dark CO₂ metabolism were measured in seeds ofBrassica campestris L. cv. Toria at different stages of pod/seed development. The period between 14 and 35 days after anthesis corresponded to active phase of seed development during which period, seed dry weight and oil content increased sharply. Rate of pod photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were maximum in younger pods but sufficiently high levels were retained up to 40 days after anthesis. The rate of dark¹⁴CO₂ fixation in seeds increased up to 21 days after anthesis and declined thereafter but maintaining sufficiently high rates till 35 days after anthesis. Similarly various enzymes viz., phosphoenolpyruvate carboxylase, NAD⁺-malate dehydrogenase and NADP⁺-malic enzyme, involved in dark CO₂ metabolism retained sufficient activities during the above period. These enzyme activities were more than adequate to maintain the desired supply of malate which mainly arises from dark CO₂ fixation in seeds and further translocated to leucoplasts for onward synthesis of fatty acids. Enzyme localization experiments revealed phosphoenolpyruvate carboxylase and enzymes of sucrose metabolism to be present only in cytosol, whereas enzymes of glycolysis were present both in cytosolic and leucoplastic fractions. These results indicated that oil synthesis in developingBrassica seeds is supported by pod photosynthesis and dark CO₂ fixation in seeds as the former serves as the source of sucrose and the latter as a source of malate     

Seed abortion in wind-dispersed pods of Dalbergia sissoo: maternal regulation or sibling rivalry?

Summary Dalbergia sissoo, a wind-dispersed tropical tree, shows a positively skewed distribution of seeds per pod. This is attributed to the enhanced dispersal advantage of few-seeded pods due to their reduced wing loading (ratio of weight to pod surface area) and low settling velocity. The proximate mechanisms causing the positively skewed distribution were investigated. The distribution could not be attributed to the distribution pattern of ovule number per ovary, pollen grain limitation, lack of ovule fertilization, or post-fertilization elimination of many-seeded pods. Rather, it was caused by the post-fertilization abortion of seeds within a pod 2 weeks after fertilization. This intra-pod seed abortion (IPSA) is due to a dominance hierarchy of fertilized ovules from the distal (near stigma) to the basal end, generated by the temporal differences in fertilization. The dominant developing seeds at the distal end cause the abortion of others through the production and diffusion of an aborting agent. When the dominance hierarchy of the siblings is not intense, pods are formed with more than one seed. We argue that the positively skewed distribution of seeds per pod is not due to maternal regulation but is a result of sibling rivalry. We propose that this sibling rivalry is generated by genetic differences in pollen grain fitness and disucss the results in the context of parent-offspring conflict.     

Seed, cutting and air-layering reproductive inefficiency of noxious woody vine Merremia biosiana and its implications for management strategy

Merremia boisiana (Gagnep) van Ooststr. is a noxious fast growing woody vine and is able to grow overtop other plants, causing the death of plants underneath and forming monospecies stands. To formulate management responses, we assessed its seed and vegetative reproduction efficacy through indoor and field experiments. The number of flowers counted from bagged infructescences in Guangzhou ranged from 25 to 172, with an average of 80.80. Counting the seeds of bagged infructescences had shown that there were only 1.58 hard testa seeds in each infructescence. Seed vitality tests using red ink indicated that only 68.6% of hard testa and filled seeds were viable. The emergence rate of scarified hard testa seeds in the sand bed was 31.96%. Under imitated natural conditions, 8% of hard testa seeds could germinate, and 9% still retained their germination potential in one year. Thus, seedlings should be monitored and removed in a timely fashion after any attempt of clearing. Moving soil or transplanting plant from infested patches should be strictly prohibited at least for several years. All considered, an infructescence contributed 0.3 seedlings. The investigation in the field found no seedlings either inside or at the perimeter of the patch, suggesting scant expansion by means of seed dispersal. Therefore, the elimination effort could be focused on a relatively restricted scale of patches. Of 630 cuttings of young shoots, old shoots and old lying shoots with or without growth regulators, there were only four (or 0.63%) established individuals. Air-layering shoots all died in two months. Poor cuttings and air-layering reproduction indicated that regeneration from fragments of removed stems or accidentally dropped ones was quite unlikely, and thus mechanical removal was safe.     

Seed production and seed predation in a patchy and time-varying environment. Dynamics of a milkweed — tephritid fly system

Summary Vincetoxicum hirundinaria is a longlived perennial herb. Its pod production was measured during seven years in about 40 small isolated patches in two study areas in southeastern Sweden. Total pod production in the two areas varied synchronously and up to about 200 times between years. This variation was mainly due to drought conditions as determined by the interplay of weather (sunshine h) and site characteristics.Populations of a univoltine tephritid fly, euphranta connexa, whose larva feeds on V. hirundinaria seeds in the maturing pods, were monitored for five and seven years in the two study areas respectively. Larval fly populations in the two areas varied 30 and 50-fold between years, with highs in years when pods were abundant and lows when pods were scarce. The percentage of pods attacked by E. connexa, however, varied in the opposite direction, with very high attack rates (about 100%) when pods were scarce and low rates (down to 10–20%) when pods were common. Thus the temporal tracking of food resources by E. connexa was poor, resulting in yearly variations in the amount of unattacked pods (and seeds) being about 2,00-fold.Many host plant patches were small and totally without pods in some years, causing frequent local extinctions of E. connexa. Patches were, however, readily colonized in later years when pods appeared again. Low overall attack rates in certain years were thus only to a minor extent explainable by host plant patches being uncolonized by the fly. The efficient spatial tracking of resources by the fly population allows this population system to be analyzed largely in terms of its temporal dynamics.Although E. connexa populations often exploit only a minor part of their potential larval resources, the rate of population change was closely correlated with these resources expressed on a per capita basis. Natural enemies only have negligible effects on E. connexa population trends. In this population system the herbivore (seed predator) population is thus controlled by its food resources, but weather-imposed temporal variations in resource set are too large for the herbivore population to closely track its resource base. This temporal tracking inertia has important implications for the long-term production of healthy seeds.     

Seed abortion in Pongamia pinnata (Fabaceae)

In Pongamia pinnata only one of the two ovules develops into a seed in most of the pods. Since pollen was not found to be limiting and reduced fertilization could not completely explain the observed frequency of seed abortion, it implied an effect of postfertilization factors. Aqueous extracts of developing seeds and maternal tissue (placenta) did not influence abortion in vitro, suggesting that abortion may not be mediated by a chemical. Experimental uptake of ¹⁴C sucrose in vitro indicated that both the stigmatic and the peduncular seed have similar inherent capacities of drawing resources, but the peduncular seed is deprived of resources in the presence of the stigmatic seed. This deprivation of the peduncular seed could be offset by supplying an excess of hormones leading to the subsequent formation of two seeds in a pod. The prevalence of single-seeded pods in P. pinnata seems therefore to be a result of competition between the two seeds for maternal resources. The evolutionary significance of single-seeded pods in P. pinnata is discussed with respect to possible dispersal advantage enjoyed by such pods.     

Assessment of the Biological Control Impact of Seed Predators on the Invasive Shrub Acacia nilotica (Prickly Acacia) in Australia

An impact assessment study was undertaken to determine seed predation rates by two bruchid beetles, Bruchidus sahlbergi Schilsky and Caryedon serratus Olivier, on the invasive shrub Acacia nilotica (L.) Willd. ex Del. The former bruchid was released as a biological control agent for A. nilotica, whereas the latter is naturalized in Australia. We attempted to determine the dynamics and magnitude of bruchid predation, following a number of differing reports of their effectiveness. To investigate the importance of seed availability on bruchid numbers, we compared seed death in high- and low-seed-density habitats, both before and after pods had dropped from tree branches. Bruchid predation was initially low (<2%) in pods on tree branches in both habitats, but increased abruptly to 12% in riparian and 32% in nonriparian exclosures by the third collection date. Bruchid numbers then crashed to below 2% in both habitats, when pods dropped to the ground. B. sahlbergi predation later increased markedly (up to 65%) again at high-pod-density sites. No further increase in predation took place beyond this level. Seed predation by C. serratus was found to be minimal (<5% of seeds infested) throughout the monitoring period. We suggest that seed predation by the bruchids, prior to pod drop and removal by cattle, is insufficient to cause major impacts on A. nilotica populations. Bruchid seed damage is likely to be significant only in situations with low cattle numbers, where cattle cannot remove the majority of fallen seed pods or where cattle are excluded. Exclusion of cattle from some areas within A. nilotica-invaded landscapes to potentially increase bruchid effectiveness is proposed. The demographic impact of optimal A. nilotica seed losses is discussed.     

Resistance to the cowpea weevil (Callosobruchus maculatus) larva in pods of cowpea (Vigna unguiculata)

Thirty cowpea, Vigna unguiculata (L.) Walpers, cultivars were evaluated as intact pods to determine if any possessed resistance to the cowpea weevil, Callosobruchus maculatus (Fabr.). Pod resistance was measured as pre-establishment larval mortality (PreM); those larvae dying after egg hatch but before penetrating into the seeds, and as post-establishment within-seed mortality (PostM); those larvae dying after penetrating into the seeds. Among the 30 varieties examined, PreM ranged from 57.9% to 99.4% and PostM ranged from 6.7% to 82.6%. Ten varieties exhibited total intact pod mortality (mortality from egg hatch to adult emergence from the seed) greater than 95%.Physical measurements were made of several pod and seed characteristics to ascertain whether the observed pod resistance was due to seed factors, pod-wall factors, or to interactions between the pod and seeds. Although resistance to breakage (from handling plus pod dehiscence) is a necessary characteristic for overall pod protection against C. maculatus; other factors are also important. Among the other pod and seed characteristics measured to identify major resistance factors, seed coat thickness was the one most highly correlated with pod resistance. Our results suggest that interactions between pod-wall and seed coat characteristics play a large role in pod resistance of cowpeas to C. maculatus.     

A model for studying pollination and pod development in Brassica napus: the culture of isolated flowers

Summary A technique for cultivating isolated flowers of Brassica napus has been developed. Flowers were harvested at anthesis, the surface of their peduncles was then sterilized and they were cultivated in a hormonefree medium. We used an MS medium supplemented with 3% sucrose as a source of organic carbon. From our experiments, it was concluded that no exogenous growth regulator is required to ensure normal growth and development in vitro. The flowers, and thereafter the pods, can be kept in culture until seed maturity. After 30 days, seed development resulted in three types of seeds: (1) normal, (2) milky and (3) aborted. The results show that the number of seeds per pod was not dependent on the order of flowers on the raceme (except the first 10 flowers and flowers above row 50). Our study supports the validity of this model as an easy tool for studying pollination and early seed development.     

Seed development in Pisum

The Ih and lh _i alleles have been shown previously to reduce the level of endogenous gibberellin A₁ (GA₁) in shoots of pea (Pisum sativum L.), resulting in a dwarf phenotype compared with the wild type, cv. Torsdag (Lh). In addition, plants homozygous for the lh ⁱ allele have reduced seed yield compared with Lh (tall, wild type) and lh (dwarf) plants. In this paper we show that the lh ⁱ mutation is expressed in developing seeds and pods. Comparison of GA levels in young shoots and developing seeds of genotypes lh and lh ⁱ demonstrates that the relative severity of the two mutations varies in different tissues. Homozygous h ⁱ seeds have reduced GA levels, weigh less, and are less likely to develop to maturity when compared with Lh seeds. However, fertilization of lh ⁱ plants with Lh pollen increases seed GA levels, seed weight and seed survival, indicating that an increase in seed GA levels due to the presence of the Lh allele can restore normal seed growth. Pods developing on self-pollinated lh ⁱ plants are shorter than pods on Lh (wild type) plants, although this may be an indirect effect of the increased seed abortion of lh _i plants. Based on these results we suggest that endogenous GAs play an important role in the development of seeds of P. sativum L.Abbreviations GA_(n) gibberellin A_n We wish to thank Katherine McPherson, Peter Newman, Leigh Johnson and Peter Bobbi for technical assistance, Professor L. Mander (ANU, Canberra) and Professor B.O. Phinney (UCLA, USA) for labelled GA standards, and the Australian Research Council for financial support.     

Free amino acids in the seed and root exudates in relation to the nitrogen requirements of rhizosphere soil Fusaria

Summary The amounts of amino acids in seed exudates were generally higher than in root exudates of the same plant. The spectra and relative abundance of amino acids in both plants were similar but they were generally more abundant in cowpea exudates than in sorghum. Glutamic acid and alanine were the most abundant amino acids in the seed and root exudates of both plants. The proportions of the amino acids in the seed exudates were comparable to that stored in the seeds. Many of the major amino acids identified in the exudates were also found to support thein vitro growth ofFusarium spp. isolated from the rhizosphere and rhizoplane. This suggests that the amino acids exuded might contribute signficantly to Fusaria nutrition and its consequent predominance around the root. The significance of this pathogenesis is also discussed.