Genetic relationships within avocado (Persea americana Mill) cultivars and between Persea species

The origin of avocado (Persea americana Mill) cultivars, as well as the genetic relationships between Persea species, are not well defined and are based mainly on morphological parameters. Minisatellite DNA markers were used to analyze 24 P. americana cultivars in an attempt to define their racial allocation. DNA mixes representing the three races were evaluated and used for analysis. The allocation of 19 of the above cultivars was substantiated by the DNA markers, while new suggestions were offered regarding the remaining five. Eight cultivars, of unknown racial origin, were also examined, and a phylogenetic tree suggesting their origin is offered. Selfing progeny of five cultivars were analyzed for six morphological traits which differentiate the three races, and were compared to their parents in order to assess their origin. Eleven Persea species were analyzed, using DNA fingerprint patterns and SSR (simple sequence repeat) alleles, in order to identify the genetic relationships among the Persea species, and between them and the three P. americana races. The phylogenetic tree obtained is presented. The high value of variation between the avocado cultivars and Persea species observed in this work, suggests that the validity of race and species definition within Persea be treated with caution. Received: 3 August 1996 / Accepted: 23 August 1996     

Isolation, culture and regeneration of avocado (Persea americana Mill.) protoplasts

Protoplasts were isolated from embryogenic suspension cultures derived from avocado (Persea americana Mill.) zygotic embryos and nucellus in an enzyme digestion solution consisting of 1% cellulase Onozuka RS, 1% Macerase R10, 0.2% Pectolyase Y-23, 0.7 M mannitol. 24.5 mM CaCl₂, 0.92 mM NaH₂PO₄ and 6.25 2-[N-morpholino]ethanesulfonic acid (1.5 ml) mixed with 0.7 M MS^–8P (2.5 ml). MS^-8P medium consisted of Murashige and Skoog salts without NH₄NO₃, 1 mg l^–1 thiamine HCl, 100 mg l^–1 myo-inositol, 3.1 g l^–1 glutamine and 8P organic addenda. Medium osmolarity was adjusted with 0.15 M sucrose and 0–0.55 M mannitol. Protoplast yields of 3.5×10⁶ protoplasts g^–1 were obtained. Growth and development of the protoplasts were significantly affected by osmolarity, nitrogen source, plating density and culture medium dilution. Under optimum conditions, proembryos developed directly from embryogenic protoplasts and subsequently into somatic embryos. Optimum conditions for somatic embryo development included the culture of protoplasts at a density of 0.8–1.6×10⁵ ml^–1 in 0.4 M MS^–8P for 2–3 weeks, followed by subculture in 0.15 M MS^–8P at a diluted density of 20–40× for 1 month in darkness to obtain somatic embryos. Mature somatic embryos were recovered on semisolid medium; however, a low frequency of plantlet recovery (≤1%) from protoplast-derived somatic embryos was observed. Received: 9 February 1998 / Revision received: 4 May 1998 / Accepted: 15 May 1998     

Influence of avocado (Persea americana) Cx-cellulase on the structural features of avocado cellulose

Avocado (Persea americana Mill.) fruit produce copious quantities of the enzyme Cx-cellulase (EC 3.2.1.4) during ripening. The possibility that Cx-cellulase is able to disrupt cellulose microfibril oranization was investigated using molecular weight (M_r), x-ray diffraction, and ultrastructural analyses of cell walls from unripe avocado fruit incubated with the purified enzyme. Results indicate that Cx-cellulase causes a downshift in the M_r of unbranched cell-wall polymers in the M_r range of 10⁶–10⁷ Da. There is an increase in the proportion of crystalline cellulose, and cellulose fibrils appear to lose cohesiveness in response to enzyme activity. We propose that Cx-cellulase attacks avocado cellulose at accessible sites in the peripheral and integral noncrystalline regions of the microfibril, resulting in a loss of cohesiveness within the fibril structure and an alteration in the binding of associated cell-wall matrix polysaccharides. The initial loss of avocado mesocarp firmness during fruit ripening may be linked to the onset of Cx-cellulase activity.Abbreviations CMC carboxymethylcellulose - DMAC dimethylacetamide - DS developmental stage - M molecular weight - XG xyloglucan     

Modification of matrix polysaccharides during avocado (Persea americana) fruit ripening: an assessment of the role of Cx-cellulase

The role of C_x-cellulase (EC 3.2.1.4) in fruit ripening and softening is unknown. In the present study, avocado ( Persea americana ) fruit, a rich source of C_x-cellulase, were examined to determine if the enzyme plays a role in ripening-related hemicellulose metabolism. Hemicelluloses (4 M alkali-soluble) from avocado fruit exhibited a very broad distribution of polymer sizes and an overall decrease in M_r during ripening. Polymers affected were primarily those of large M_r (relative molecular mass). The characteristic total hemicellulose M_r distribution and changes with ripening were also evident for xyloglucan (XG), a putative substrate for avocado C_x-cellulase. Hydrolytic activity toward hemicelluloses from preripe fruit was detected in crude buffer-soluble protein extracts derived from ripe avocado mesocarp tissue. XG was also degraded, and in a pattern similar to that observed during ripening. Purified C_x-cellulase also exhibited activity against specific components of isolated hemicelluloses; however, in contrast to the crude protein. C_x-cellulase alone was without influence on the M_r distribution of avocado XG. Protein depleted of C_x-cellulase was capable of moderate XG depolymerization. We conclude from the present studies that the enzyme C_x-cellulase is not involved in the ripening-related depolymerization of XG in avocado fruit.     

Breeding biology and incremental benefits of outcrossing for the restoration wildflower,Hedysarum boreale Nutt. (Fabaceae)

Northern sweetvetch (Hedysarum boreale Nutt.) is an herbaceous perennial legume of the Rocky Mountains, USA, whose seed is desired for rehabilitating degraded plant communities. Through experimental pollinations, the necessity of pollinators was shown by the failure of autogamy, despite stigmas first becoming receptive in the bud in close proximity to the dehiscing anthers. Nonetheless, the species proved to be self‐fertile, initiating as many fruits through selfing as outcrossing. Incremental benefits of outcrossing only later manifested in superior fruit development, seed maturation and seed germination. Farming of H. boreale can yield abundant viable seed if adequately visited by pollinating bees.     

In vivo anticoccidial,antioxidant, and anti-inflammatory activities of avocado fruit,Persea americana (Lauraceae), against Eimeria papillata infection

Apicomplexan parasites, especially Eimeria sp., are the main intestinal murine pathogens, that lead to severe injuries to farm and domestic animals. Many anticoccidial drugs are available for coccidiosis, which, leads to the development of drug-resistant parasites. Recently, natural products are considered as an alternative agent to control coccidiosis. This study was designed to evaluate the anticoccidial activity of the Persea americana fruit extract (PAFE) in male C57BL/6 mice. A total of 35 male mice were divided into seven equal groups (1, 2, 3, 4, 5, 6, and 7). At day 0, all groups except the first group which served as uninfected-untreated control were infected orally with 1 × 10³ E. papillata sporulated oocysts. Group 2 served as uninfected-treated control. Group 3 was considered an infected-untreated group. After 60 min of infection, groups 4, 5, and 6 were treated with oral doses of PAFE aqueous methanolic extract (100, 300, and 500 mg/kg of body weight, respectively). Group 7 was treated with amprolium (a reference drug for coccidiosis). PAFE with 500 mg/kg, was the most effective dose, inducing a significant reduction in the output of oocysts in mice feces (by about 85.41%), accompanied by a significant decrease in the number of the developmental parasite stages and a significant elevation of the goblet cells in the jejunal tissues. Upon treatment, a significant change in the oxidative status due to E. papillata infection was observed, where the levels of glutathione (GSH) increased, while, levels of malondialdehyde (MDA) and nitric oxide (NO) were decreased. In addition, the infection significantly upregulated the inflammatory cytokines of interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), and interferon-γ (IFN-γ). This increase in mRNA expression of IL-1β, TNF-α, and IFN-γ was about 8.3, 10.6, and 4.5-fold, respectively, which significantly downregulated upon treatment. Collectively, P. americana is a promising medicinal plant with anticoccidial, antioxidant, and anti-inflammatory activities and could be used for the treatment of coccidiosis.     

Influence of pollination systems on fruit set and fruit quality in kiwifruit (Actinidia deliciosa)

Kiwifruit (Actinidia deliciosa (Chev.) Liang and Ferguson) is a dioecious species highly pollination dependent, since fruit size is directly correlated with seed number. To evaluate the best pollination system for this species a study of two natural and two artificial pollination systems was carried out and their effect on fruit set and fruit quality was determined. While anemophilous pollination produced few and small fruits, that were not commercially acceptable, high fruit set percentages and good quality fruits were obtained when insects participated in the pollination process. Artificial pollination, performed as hand pollination, improved yield quantity and quality. When environmental conditions impair insect activity this method can be an useful agricultural practice in order to assure a good yield.     

Phytogenic compounds from avocado (Persea americana L.) extracts; antioxidant activity,amylase inhibitory activity,therapeutic potential of type 2 diabetes

Diabetes is a worldwide public health disease. Currently, the most effective way to treat diabetes is to mitigate postprandial hyperglycemia by inhibiting carbohydrate hydrolysis enzymes in the digestive system. Plant extracts are rich in bioactive compounds, which can be used in diabetes treatment. This study aims to evaluate the polyphenols content in ethanolic extracts of avocado fruit and leaves (Persea americana Mill.). Additionally, their antioxidant activity using DPPH, while the inhibition ability of α-amylase was examined by reacting different amounts of the extracts with α-amylase compared to acarbose as standard inhibitor. The active compounds were detected in the extracts by LC/MS. The obtained results showed that the leaf extract recorded a significant content of total phenolic compounds compared to the fruit extract (178.95 and 145.7 mg GAE /g dry weight, respectively). The total flavonoid values ??ranged from 32.5 to 70.08 mg QE/g dry weight of fruit and leaves extracts, respectively. Twenty-six phytogenic compounds were detected in leaf and fruit extract by LC/MS. These compounds belong to fatty acids, sterols, triterpenes, phenolic acids, and flavonoids. The antioxidant activity of the extracts is due to the exist of phytogenic compounds, i.e., polyphenols and flavonoids. The antioxidant activity increased in a concentration dependant manner. Avocado fruit extract (1000 µg/mL) scavenged 95% of DPP? while leaf extract rummaged 91.03% of free radicals compared with Vit C and BHT. Additionally, higher α-amylase inhibitory activity was observed in fruit extract than the leaf extract, where the fruit and leaf extract (1000 μg/ml) inhibited the enzyme by 92.13% and 88.95%, respectively. The obtained results showed that the ethanolic extracts of avocado could have a significant impact on human health due to their high content of polyphenols.     

Integrating gene flow, crop biology, and farm management in on-farm conservation of avocado (Persea americana, Lauraceae)

Maintaining crop diversity on farms where cultivars can evolve is a conservation goal, but few tools are available to assess the long-term maintenance of genetic diversity on farms. One important issue for on-farm conservation is gene flow from crops with a narrow genetic base into related populations that are genetically diverse. In a case study of avocado (Persea americana var. americana) in one of its centers of diversity (San Jerónimo, Costa Rica), we used 10 DNA microsatellite markers in a parentage analysis to estimate gene flow from commercialized varieties into a traditional crop population. Five commercialized genotypes comprised nearly 40% of orchard trees, but they contributed only about 14.5% of the gametes to the youngest cohort of trees. Although commercialized varieties and the diverse population were often planted on the same farm, planting patterns appeared to keep the two types of trees separated on small scales, possibly explaining the limited gene flow. In a simulation that combined gene flow estimates, crop biology, and graft tree management, loss of allelic diversity was less than 10% over 150 yr, and selection was effective in retaining desirable alleles in the diverse subpopulation. Simulations also showed that, in addition to gene flow, managing the genetic makeup and life history traits of the invasive commercialized varieties could have a significant impact on genetic diversity in the target population. The results support the feasibility of on-farm crop conservation, but simulations also showed that higher levels of gene flow could lead to severe losses of genetic diversity even if farmers continue to plant diverse varieties.     

Reproductive biology of the invasive exotic shrub, Rhododendron ponticum L. (Ericaceae)

The reproductive biology of an exotic species will affect its ability to become naturalized and invasive in non-native habitats. Rhododendron ponticum is an ecologically damaging exotic weed in the British Isles, which spreads predominantly by seed. I investigated how inbreeding and outcrossing affect seed production and germination in a wild population of this species in Ireland. Experimental manipulations revealed low fruit and seed set when insects were excluded from flowers, suggesting that this species has limited capability for spontaneous autogamy. Hand-pollination treatments showed that, although flowers are self-compatible (with self and same plant pollen), higher levels of seed set occur following outcrossing (xenogamy). There was no significant difference in rate of germination of seeds from inbred or outcrossed treatments. The addition of xenogamous pollen to open flowers did not increase fruit or seed set, suggesting that flowers in this population are not pollen limited: native generalist pollinators, mainly bumblebees ( Bombus spp.), are providing an adequate pollinator service. This work demonstrates that outcrossing increases seed set and pollinators are required to facilitate this. Hence, generalist native pollinators can promote invasion by exotic plants. Native pollinators can clearly play an important part in alien species invasion.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 373–381.     

The importance of avocado (Persea americana Mill.) fruits anthracnose and factors influencing the disease in Mana district,south-western Ethiopia

Anthracnose disease surveys were conducted in 25 farmers’ orchards, wholesaler and retailer shops in south-west Ethiopia. In addition, harvesting and postharvest practices, and storage conditions influencing disease development were studied with observation and questionnaire. The assessment results indicated significant variation among farmers’ orchards with the highest incidence (84.0 ± 16.7%) and severity index (26.0 ± 5.4%). Anthracnose damage of fruit was higher at retailers (76.7 ± 20.8%) than in the wholesalers shop (56.7 ± 32.5%). The total number of isolates identified was 249 and Colletotrichum gloeosporioides was the predominant pathogen proved by pathogenecity test. Among the major factors, harvesting avocado fruits with children (88%) and climbing on the tree (72%) resulted in fruit dropping that caused substantial injury and bruise. Generally, anthracnose caused by C. gloeosporioides of avocado fruit was prevalent in producer orchards that aggravated by traditional harvest and postharvest practices coupled to inadequate transportation and storage facilities at wholesaler and retailer shops with subsequent decay and loss of avocado fruits.     

Short- and long-term modulation of the lutein epoxide and violaxanthin cycles in two species of the Lauraceae: sweet bay laurel (Laurus nobilis L.) and avocado (Persea americana Mill.)

Short- and long-term responses of the violaxanthin (V) and lutein epoxide (Lx) cycles were studied in two species of Lauraceae: sweet bay laurel (Laurus nobilis L.) and avocado (Persea americana L.). The Lx content exceeded the V content in shade leaves of both species. Both Lx and V were de-epoxidised on illumination, but only V was fully restored by epoxidation in low light. Violaxanthin was preferentially de-epoxidised in low light in L. nobilis. This suggests that Lx accumulates with leaf ageing, partly because its conversion to lutein is limited in shade. After exposure to strong light, shade leaves of avocado readjusted the total pools of alpha- and beta-xanthophyll cycles by de novo synthesis of antheraxanthin, zeaxanthin and lutein. This occurred in parallel with a sustained depression of F(v)/F(m). In Persea indica, a closely related but low Lx species, F(v)/F(m) recovered faster after a similar light treatment, suggesting the involvement of the Lx cycle in sustained energy dissipation. Furthermore, the seasonal correlation between non-reversible Lx and V photoconversions and pre-dawn F(v)/F(m) in sun leaves of sweet bay supported the conclusion that the Lx cycle is involved in a slowly reversible downregulation of photosynthesis analogous to the V cycle.     

Relationships between plant density,outcrossing rates and seed set in natural and experimental populations of Scabiosa columbaria

Outcrossing rates were estimated in both natural and experimental populations of Scabiosa columbaria, a self-compatible, entomophilous, gynodioecious, protandrous perennial. In natural populations, estimates of the outcrossing rate in hermaphrodites were near to one and ranged from 0.84 ± 0.07 to 1.12 ± 0.11. The effect of plant density on outcrossing rates was studied in two experimental populations of 27 individuals. Contrary to expectation the estimates of the outcrossing rate in hermaphrodites were about 100% for both densities. However, in the sparse population, the fraction of developed seeds of plants used to estimate outcrossing rates was significantly lower than of plants in the dense population (0.41 ± 0.06 and 0.68 ± 0.08, respectively). Artificial pollinations of these plants in the greenhouse showed that the fraction of developed seeds was 0.60 ± 0.01 and 0.83 ± 0.05 after self- and cross-pollination, respectively. The combined results suggested that the differential success of self- and cross-pollination might have caused equalization of the outcrossing rates in the experimental populations, despite different plant densities. The implications of the results for conservation biology are discussed.     

Methyl de-esterification as a major factor regulating the extent of pectin depolymerization during fruit ripening: a comparison of the action of avocado (Persea americana) and tomato (Lycopersicon esculentum) polygalacturonases

Pectinmethylesterase (PME, EC 3.2.1.11) and polygalacturonase (PG, EC 3.2.1.15) are known to operate in tandem to degrade methylesterified polyuronides. In this study, PGs purified from tomato and avocado fruit were compared in terms of their capacity to hydrolyze water-soluble polyuronides from avocado before and following enzymic or chemical de-esterification. When assayed using polygalacturonic acid or polyuronides from avocado fruit, the activity of PG from tomato fruit was 3-4 times higher than that from avocado fruit. High molecular mass, low methylesterified (33%) water-soluble polyuronides (WSP) from pre-ripe avocado fruit (day 0) were partially depolymerized upon incubation with purified avocado and tomato PGs. In contrast, middle molecular mass, highly methylesterified (74%) WSP from day 2 fruit were largely resistant to the action of both PGs. PME or weak alkali treatment of highly methylesterified WSP decreased the methylesterification values to 11 and 4.5%, respectively. Treatment of de-esterified WSP with either avocado or tomato PGs caused extensive molecular mass downshifts, paralleling those observed during avocado fruit ripening. Although PME and PG are found in many fruits, the pattern of depolymerization of native polyuronides indicates that the degree of cooperativity between these enzymes in vivo differs dramatically among fruits. The contribution of PME to patterns of polyuronide depolymerization observed during ripening compared with physically compromised fruit tissues is discussed.     

Evidence for the presence of a native,non-auxinic rooting promoter in avocado (Persea americana Mill.)

The presence of a rooting promoter in paratially purified extracts of avocado (Persea amricana Mill.) organs has been demonstrated using the mung bean rooting bioassay. Extraction with 80% methanol was followed by partition into diethyl ether, paper chromatography (PC) and 3 steps of thin layer chromatography (TLC). The number of roots induced by the rooting promoter in the absence of exogenous auxin was 5 to 7 times higher than that of the water control and 50% higher than by 4-(indol-3-yl) butyric acid (IBA) at its reported optimum concentration. Rooting of tomato, Coleus and young avocado cuttings was also enhanced by the rooting promoter. The rooting promoter was inhibitory in the wheat coleoptile section elongation bioassay for auxins and had slight inhibitory activity in the split pea stem curvature test.The biological properties of the avocado rooting promoter may be comparable to those of -(p-chlorophenoxy) isobutyric acid (PCIB) which acts as an anti-auxin in certain bioassays and, nevertheless, promotes the rooting of mung bean cuttings.     

大棚油桃授粉方式研究初报

2002年2-5月,研究利用蜜蜂、壁蜂花期传粉及人工授粉技术对大棚油桃艳光和潍甜1号的座果率及产量均有不同程度的提高;其中潍甜1号的座果率提高幅度最大。上述几种方法中,人工授粉的效果最好。     

Influences of Cross Pollination on Pollen Tube Growth and Fruit Set in Zuili Plums （Prunus salicina）

Zuili plum （Prunus salicina L.） trees usually set fruit poorly, although they produce high quality fruit. To elucidate the causes of the poor fruit set, pollen tube growth into pistils and fruit set percentage were investigated after cross-, self- and open-pollination. Ovule development in Zuili pistils was also investigated. Pollen tube penetration into the ovules via the obturator and micropyle was best when Zuili pistils were pollinated by cv. Black Amber （P. domestica） pollen grains, although cross-pollinations with Hongxinli and Miili （P. salicina） pollen were more effective than self- and open-pollination. The fruit set percentage was also highest in pistils pollinated with Black Amber pollen grains. Morphological observation of Zuili pistils revealed that the trees produce ＂double pistils＂, developing two ovaries from a basal pistil, at a rate as high as 28%. In such abnormal pistils, most ovules were lacking an embryo sac or were entirely degenerated. The percentage of normally developed ovules was 24.3% and 8.9% in normal and double pistils, respectively. From these results, we conclude that the main causes of poor fruit set of Zuili plums are a lack of effective cross-pollination and the production of high percentages of double pistils in which normally developed ovules are scarcely formed.     

Causes of spatial patterns of fruit set in waratah: Temporal vs. spatial interactions between flowers on an inflorescence

Spatial patterns of fruit set within inflorescences may be controlled by pollination, nutrient allocation, or inflorescence architecture. Generally, flowers that have spatial and/or temporal precedence are more likely to set fruits. We sought to separate these factors by comparing patterns of fruit set on inflorescences of two species of Telopea (Proteaceae); one that flowers from the tip to the base of the rachis, the other from base to tip. In both species, most fruits were set at the top of the inflorescence (the last flowers to open for T. speciosissima) and this was extreme for T. mongaensis, where the top flowers open first. Fruit set was not generally limited by inadequate pollination for either T. mongaensis or T. speciosissima, as hand pollinations did not increase fruit set and many abscised flowers contained pollen tubes. In T. speciosissima, we tested whether removal of developing topmost fruits would ‘release’ those that had initiated but not yet aborted lower down. There was no significant effect. Plant hormones can increase the degree to which a developing fruit is a sink for nutrients, so we applied cytokinin to the developing lower fruits on some inflorescences. There was no significant effect of the hormone treatment. We conclude that temporal precedence may contribute to the skewed pattern of fruit set in T. mongaensis, because there was an extreme concentration of fruit set on the distal part of the inflorescences, but it cannot explain this pattern of fruit set in T. speciosissima, where the distal flowers are the last to open. Some other process must therefore constrain fruit set to the topmost flowers in an inflorescence. While cytokinin application had no significant effect, the power of this experiment was low and we consider that the hypothesis of hormonal control is worth further exploration.     

Reproductive ecology of three endangered African violet (Saintpaulia H. Wendl.) species in the East Usambara Mountains, Tanzania

Knowledge of the reproductive biology of endangered plants is essential for their effective conservation. It also provides important information for understanding the evolutionary processes that affect speciation, thus helping the definition of proper units for conservation in endangered plants with problematic taxonomy. We studied the reproductive potential and possibility for hybridization in the endangered genus Saintpaulia (Gesneriaceae) by examining flowering phenology, flower and seed production and pollination of three sympatric cross‐compatible Saintpaulia species in the East Usambara Mts., Tanzania. The synchrony observed in flowering in S. confusa and S. difficilis may enable hybridization between these two species, whereas partial phenological separation may contribute to the integrity of S. grotei. Although the level of flower abortion is high in S. confusa, each pollinated flower yields about 1000 seeds. Saintpaulia confusa produces fruits following both self‐ and cross‐pollination but spontaneous self‐pollination seems not to occur. Thus, seed production depends on sufficient pollinator service. Floral heteromorphy (i.e. enantiostyly) and bee pollination are likely to further enhance cross‐pollination, suggesting that the genus predominantly outcrosses. Thus, Saintpaulia populations are likely to suffer from negative effects of inbreeding if they become small and isolated.     

Effects of self-, chase and mixed self/cross-pollinations on pistil longevity and fruit set in Ceiba species (Bombacaceae) with late-acting self-incompatibility

BACKGROUND AND AIMS: Late-acting self-incompatibility (LSI), in which selfed flowers fail to form fruits despite apparently successful growth of the pollen tubes to the ovules, is a contentious and still poorly understood phenomenon. Some studies have indicated pollen tube-pistil interactions, and major gene control. Others favour an early acting inbreeding depression explanation. METHODS: Experimental pollinations, including selfs (in a subsample of which the style was cut before pollen tubes reached the ovary), chase self/cross-pollinations, crosses, and mixed self/cross-pollinations were used to study floral/pistil longevity and effect on fruit set and seed yield in two Ceiba species known to have LSI. RESULTS: Self-pollinations, including those with a cut style, had extended floral longevity compared with unpollinated flowers. Chase pollinations in which cross-pollen was applied up to 3 h after selfing set fruits, but with reduced seed set compared with crosses. Those with cross-pollen applied at 4 and 8 h after self-pollination all failed to set fruits. Flowers subjected to 1 : 1 and 2 : 1 self/cross-pollinations all produced fruits but again with a significantly lower seed set compared with crosses. CONCLUSIONS: Extended floral longevity initiated with self-pollen tubes growing in the style indicates some kind of pollen tube-pistil interaction. Fruit set only in chase pollinations up to 3 h implies that self-pollen tubes either grow more slowly in the style or penetrate ovules more slowly on arrival at the ovary compared with cross-tubes. This agrees with previous observations indicating that the incidence of penetrated ovules is initially lower in selfed compared with crossed pistils. However, the low seed yield from mixed pollinations indicates that self- and cross-pollen tubes arrive at the ovary and penetrate ovules more or less simultaneously. Possible explanations for these discordant results are discussed.