Genetic relationships and evolution in <Emphasis Type="Italic">Cucurbita pepo</Emphasis> (pumpkin,squash, gourd) as revealed by simple sequence repeat polymorphisms

Genetic relationships among 104 accessions of Cucurbita pepo were assessed from polymorphisms in 134 SSR (microsatellite) and four SCAR loci, yielding a total of 418 alleles, distributed among all 20 linkage groups. Genetic distance values were calculated, a dendrogram constructed, and principal coordinate analyses conducted. The results showed 100 of the accessions as distributed among three clusters representing each of the recognized subspecies, pepo, texana, and fraterna. The remaining four accessions, all having very small, round, striped fruits, assumed central positions between the two cultivated subspecies, pepo and texana, suggesting that they are relicts of undescribed wild ancestors of the two domesticated subspecies. In both, subsp. texana and subsp. pepo, accessions belonging to the same cultivar-group (fruit shape) associated with one another. Within subsp. pepo, accessions grown for their seeds or that are generalists, used for both seed and fruit consumption, assumed central positions. Specialized accessions, grown exclusively for consumption of their young fruits, or their mature fruit flesh, or seed oil extraction, tended to assume outlying positions, and the different specializations radiated outward from the center in different directions. Accessions of the longest-fruited cultivar-group, Cocozelle, radiated bidirectionally, indicating independent selection events for long fruits in subsp. pepo probably driven by a common desire to consume the young fruits. Among the accessions tested, there was no evidence for crossing between subspecies after domestication.     

Inbreeding influences herbivory in <Emphasis Type="Italic">Cucurbita pepo</Emphasis> ssp. <Emphasis Type="Italic">texana</Emphasis> (Cucurbitaceae)

In a series of field experiments Diabrotica beetle herbivory was found to influence the magnitude of inbreeding depression in Cucurbita pepo ssp. texana, an annual monoecious vine. Beetles damage flowers and fruits and chew dime-sized holes in leaf tissue between major veins. Inbred plants were found to be more likely to be damaged by beetles and to have more leaves damaged per plant than outcrossed plants. A positive linear association was found between the coefficient of inbreeding and the magnitude of leaf damage, whereas a negative association was found between coefficient of inbreeding and several male and female fitness traits. When pesticides were used to control beetle herbivory, the interaction between coefficient of inbreeding and pesticide treatment was significant for fruit production and marginally significant for pollen quantity per anther. Therefore, the magnitude of inbreeding depression in C. pepo ssp . texana varies depending on the severity of beetle herbivory.     

Cytokinins antagonize the jasmonates action on the regulation of potato (Solanum tuberosum) tuber formation in vitro

Cucurbita pepo L. (squash, pumpkin) is a highly polymorphic vegetable species of major importance. Our study characterized a spectrum of C. pepo germplasm for the ability to regenerate in vitro by direct organogenesis from cotyledon explants. Cultivars tested included both cultivated subspecies, texana and pepo, and nearly all of their respective cultivar-groups. Direct shoot regeneration occurred in all accessions, and was generally high (56–94%), with a single exception of 22% (‘Bolognese’). There was no significant difference between the percentage regeneration of the two subspecies. Shoot regeneration per responding explant was uniform (1.2–1.6 shoots per explant). Only ‘True French’ produced statistically more shoots (3.9 per explant) than other accessions. The morphology of regeneration varied. Most cultivars produced long shoots, often fasciated, amid a few small buds. Some subspecies pepo cultivars (Beirut, Yugoslavia 7, Ma’yan and True French) produced short, massive, hollow shoots, sometimes accompanied by shoots that were more normal. Two subspecies texana cultivars (Creamy Straightneck and Small Bicolor) produced single (sometimes double) shoots without other buds. The production of chimeric (mixoploid) regenerants varied and there was a tendency to regenerate chimeric plants from the widest-fruited accessions (i.e. lowest length-to-width ratio) in each subspecies. Subspecies pepo Pumpkin Group ‘Tondo di Nizza’ showed significantly greater production of chimeric regenerants. In comparison with the great range of variation observed in fruit shape, the variation of in vitro responses (mostly less than 2-fold in regeneration and shoot production) was less than expected.     

Phylogenetic relationship and germplasm evaluation of different taxa of the genus Cucurbita using seed storage protein profiling

Seed protein profiling of 34 lines of Cucurbita pepo L. from different geographic regions of the world were evaluated for their polypeptide patterns and their phylogenetic relationship with other taxa of the genus Cucurbita. Considerable variations were observed in the polypeptide patterns of various lines on the SDS-polyacrylamide gels under reduced conditions, i.e. seed protein extract with 2-mercaptoethanol. The variations were observed in five different molecular weight regions, i.e. in the range 64–70, 53–60, 30–41, 20–26 and 18–20 kDa. Cluster analysis showed 100% genetic similarity between C. pepo and C. pepo var. pepo whereas it is quite distinct from C. pepo var. texana and C. pepo var. fraterna. On the basis of electrophoretic profiling C. pepo var. texana and C. pepo var. fraterna should be considered as different species and also supports the origin of C. pepo from C. texana.     

Digestion of fruit of invasive alien plants by three southern African avian frugivores

Many highly invasive plants are fleshy‐fruited and owe their invasiveness largely to mutualisms formed with local dispersers. The energetic benefits gained by frugivores from ingestion of fruits of invasive alien plants remain poorly documented. We assess whether avian frugivores process fruits of invasive alien plants effectively to meet their daily energetic requirements. Four fleshy‐fruited plant species that are invasive in southern Africa were considered –Solanum mauritianum, Cinnamomum camphora, Lantana camara and Psidium guajava. Their fruits were fed to three common generalist frugivores – Red‐winged Starling Onychognathus morio, Speckled Mousebird Colius striatus and Dark‐capped Bulbul Pycnonotus tricolor– to determine the efficiency of digestion. Energetic parameters calculated for all fruit diets varied significantly between frugivore species. Speckled Mousebirds and Dark‐capped Bulbuls maintained body mass and efficiently processed all four fruit types, whereas Red‐winged Starlings only did so on C. camphora and S. mauritianum diets. These results explain why these fruits are attractive to local avian frugivores. Furthermore, these avian frugivores processed large quantities of invasive fruits, thereby serving as potentially efficient dispersers.     

Factors affecting the phytoaccumulation of weathered, soil-borne organic contaminants: analyses at the ex Planta and in Planta sides of the plant root

Persistent Organic Pollutants (POPs) in the soil–plant system were tracked from their origin in the bulk soil, into the rhizosphere soil pore water, to the xylem sap, and up to the aerial plant tissue. Specifically, the profiles of both chiral and achiral components of technical chlordane along this continuum were examined in detail for members of the Cucurbitaceae family: Cucurbita pepo L. subsp. pepo (“Black Beauty” true zucchini), Cucurbita pepo L. intersubspecific cross (“Zephyr” summer squash), and Cucumis sativus (“Marketmore” cucumber). The experiments were based on the use of mini-rhizotrons for collection and analysis of rhizosphere soil pore water for organic pollutants, as well as for low molecular weight organic acids (LMWOAs). In addition, the xylem sap and aerial plant tissue for intact, homografted, and heterografted C. pepo “Black Beauty” and C. sativus “Marketmore” plants were compared. The data indicate that profiles of the chlordane components in the pore water show no alteration in chiral patterns from those in the bulk soil and may be interpreted by physicochemical partitioning coefficients. Low molecular weight organic acids (LMWOAs) in the rhizosphere were observed to have a minor impact on bioavailability of the pollutants. However, once the pollutants cross the root membrane, major distinctive uptake and enantioselective patterns are apparent in the xylem sap, which are maintained in the aerial tissue. These in planta patterns are based on plant genotype. Specifically, grafting experiments with compatible heterografts of C. pepo and C. sativus establish that the chiral patterns are fully dependent on the plant root. The genotypic dependence of the data suggests possible mechanisms for phytoaccumulation.     

Resistance to Tomato leaf curl New Delhi virus in Cucurbita spp.

Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus (family Geminiviridae) first reported in India and its neighbouring countries. ToLCNDV severely affects zucchini crop (Cucurbita pepo) in the main production areas of Southern Spain since 2012. This emerging begomovirus is a serious threat to this and other cucurbit crops. Breeding resistant cultivars is the most promising method for disease control, but requires the identification of sources of resistance in the Cucurbita genus. In this work, we screened for ToLCNDV resistance a large collection of Cucurbita spp. accessions, including landraces and commercial cultivars of the main cultivated species, C. pepo, Cucurbita moschata and Cucurbita maxima and wild species. The screening was performed using mechanical and whitefly inoculation. The level of resistance was assessed by scoring symptom severity and by measuring the virus content with quantitative polymerase chain reaction in selected genotypes. Diversity in the response was observed within and among species. Severe symptoms and high viral amounts were found at 30 days after mechanical and whitefly inoculation in C. pepo, in all accessions belonging to the Zucchini morphotype and to other morphotypes of both subspecies, pepo and ovifera, and even in the wild relative Cucurbita fraterna. C. maxima was also highly susceptible. This species showed characteristic symptoms of leaf decay and intense yellowing, different from those of mosaic, curling and internode shortening found in C. pepo. The only species showing resistance was C. moschata. Four accessions were symptomless or had some plants with only mild symptoms after three independent rounds of mechanical inoculation with different inoculum sources. Two of them also remained symptomless after virus inoculation with viruliferous whiteflies. ToLCNDV was detected in these asymptomatic accessions at 15 and 30 days post inoculation, but viral amounts were much lower than those found in susceptible genotypes, suggesting a high level of resistance. The symptoms in the susceptible accessions of this species were also different, with a characteristic leaf mottling, evolving to a severe mosaic. The newly identified C. moschata resistant accessions are good candidates for breeding programmes to avoid the damage caused by ToLCNDV.     

Chloroplast DNA diversity among wild and cultivated members of Cucurbita (Cucurbitaceae)

Summary Cladistic analysis of 86 chloroplast DNA restriction-site mutations among 30 samples representing 15 species of Cucurbita indicates that annual species of the genus are derived from perennials. The Malabar Gourd, C. ficifolia, is placed as a basal, sister taxon relative to other domesticated species and allied wild-types. The pattern of variation supports three species groups as monophyletic: (1) C. fraterna, C. pepo, and C. texana, (2) C. lundelliana, C. martinezii, C. mixta, C. moschata and C. sororia, and (3) C. foetidissima and C. pedatifolia. Domesticated samples representing subspecies of C. pepo are divided into two concordant groups, one of which is allied to wild-types referable to C. texana and C. fraterna. The data failed to resolve relationships among cultivars of C. moschata and C. mixta and their association to the wild C. sororia. The South American domesticate, C. maxima, and its companion weed, C. andreana, show close affinity and alliance to C. equadorensis.     

Origin(s), evolution,and systematics ofCucurbita pepo (Cucurbitaceae)

Numerical studies of morphological data and starch gel electrophoresis have provided a new perspective on important issues pertinent to the origin(s) and subsequent evolution of domesticatedCucurbita pepo. Wild C.texana and/orC. fraterna appear to be the most likely candidates for progenitor(s) of the domesticate. Populations of texana-like plants from beyond Texas share various attributes with Texas populations, suggesting that C. texana once had a more widespread distribution to the northeast. The possibility exists thatC. pepo was domesticated independently in eastern U.S., as well as in Mexico, which is in line with recent archeological findings. Multiple domestications are also supported by allozyme data indicating a substantial divergence within the species. A new classification consisting of C.pepo ssp.pepo (origins in Mexico),C. pepo ssp.ovifera var. ovifera (origins in eastern U.S.), and C.pepo ssp.ovifera var. texana (spontaneous populations in eastern U.S.) is proposed.     

Xylem transport interruption byAnasa tristis feeding causesCucurbita pepo to wilt

The plant tissues ingested byAnasa tristis (DeGeer) (Heteroptera: Coreidae) and the wilting ofCucurbita pepo L. (Cucurbitaceae) caused byA. tristis were investigated by feeding and light microscopy studies.Anasa tristis ingests both cell contents and xylem. Wilting of leaves and young plants byA. tristis is due to the interruption of all xylem transport to the plant apical to the feeding site. Xylem transport is interrupted by blockage, of xylem vessels with salivary secretions or severing of xylem vessels byA. tristis stylets. Restricting feeding sites by caging demonstrates that squash bug does not produce a toxin that is responsible for wilting.     

Effects of developmental heat sum on fruit traits of clonal lines of <Emphasis Type="Italic">Quercus petraea</Emphasis> grown under controlled conditions

An analysis was made of fruit traits of grafted lines of the recalcitrant fruited species Quercus petraea. Plants were grown either inside or outside a glasshouse in Denmark to test the impact of heat sum on fruit development. The results indicated that across the grafted lines, fruits from plants inside the glasshouse were consistently larger with a lower water content. This suggests that fruit development progressed further within phase II of development. This is consistent with findings from earlier, uncontrolled experiments and provides a quantitative explanation for intra-species variability in fruit / seed traits for recalcitrant seeded species.     

Purification and Identification of a South African Isolate of Watermelon Mosaic Virus – Morocco

Cucurbit crops in South Africa are seriously affected by a flexuous rod-shaped virus 706 to 770 nm long which causes the plant to be stunted, the leaves to display symptoms of chlorotic mosaic, dark green blisters and malformation, and fruit to be malformed. The virus was purified from infected Cucurbita pepo by extraction in 0.5 M borate buffer, pH 8, containing ethylenediaminotetra-acetic acid and mercapto-ethanol, clarification with chloroform, addition of Triton X-100, sedimentation by ultracentrifugation for which a sucrose cushion was used and centrifugation in 10 to 40 % sucrose gradients. The virus was mechanically transmitted to a limited host range with Chenopodium album, C. amaranticolor, C. quinoa and Gomphrena globosa being the only hosts infected outside the Cucurbitaceae. Luffa cylindrica, Cucumis metuliferus, Coccinia sessilifolia and Citrullus ecirrhosus all members of the Cucurbitaceae, were not infected by the virus. The virus was non-persistently transmitted by Myzus persicae, produced pinwheel and bundle inclusions in the plant cell cytoplasm and has a single coat protein with a molecular weight of 36,000 daltons and a degraded lighter component of 26,000 daltons. Serological comparisons with antiserum to watermelon mosaic virus 2, Papaya ringspot virus strain W and watermelon mosaic virus Morocco (WMV-Mor.) identified the virus as an isolate of WMV-Mor. It was found that WMV-Mor. is the dominant virus in all the main cucurbit producing areas of South Africa which were surveyed.     

Response of female melon fly, Bactrocera cucurbitae, to host-associated visual and olfactory stimuli

In a series of studies conducted in Hawaii under seminatural conditions, we quantified the response of sexually mature, host‐seeking female melon flies, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), to different types of visual and chemical host‐associated stimuli with the main aim of developing a monitoring device for females. Experiments were conducted using Tangletrap‐coated fruit mimics of either spherical (8 cm diameter) or cylindrical (4.3 cm diameter; 15 cm length) shapes coated with different artificial color pigments both at the ground level and at the tree‐canopy level so as to take into account the foraging behavior of adult melon flies. Females were particularly attracted to objects of spherical shape colored either yellow, white, or orange; these three pigments offered the highest reflectance values. Cucumber (Cucumis sativus L.) (Cucurbitaceae) odor was more attractive to females than odors of three other cultivated host fruit [zucchini, Cucurbita pepo L. var. medullosa Alef. (Cucurbitaceae); papaya, Carica papaya L. (Caricaceae); or tomato Solanum lycopersicum L. (Solanaceae)] or of ivy gourd [Coccinia grandis (L.) Voigt (Cucurbitaceae)], one of the major wild hosts of melon fly in Hawaii. A combination of both visual and olfactory stimuli was needed to elicit high levels of response compared to each stimulus offered alone. We discuss our results in relation to the potential implementation of improved female monitoring and/or attract‐and‐kill strategies for melon flies in Hawaii.     

Historical records,origins, and development of the edible cultivar groups ofCucurbita pepo (Cucurbitaceae)

Cucurbita pepo includes eight groups of edible cultivars—pumpkins, scallops, acorns, crooknecks, straightnecks, vegetable marrows, cocozelles, and Zucchinis. The pumpkins, scallops, and possibly the crooknecks are ancient groups that developed along separate lines of domestication in North America. Incipient forms of all the other five groups appeared in botanical herbals of Europe by 1700. Modern forms of the vegetable marrows, cocozelles, Zucchinis, and acorns appeared in Europe prior to 1860, and the modern straightnecks appeared in North America by 1896. Divergence among the various groups appears to be increasing under continuing domestication due to the different demands made on cultivars grown for their immature fruits as opposed to cultivars grown for their mature fruits. An association exists between length to width ratio and stage of culinary use of the fruits inCucurbita pepo.     

INTERSPECIFIC GENE FLOW IN CUCURBITA: C. TEXANA VS. C. PEPO

The potential for interspecific genetic exchange was examined by monitoring flowering patterns, pollinator movement, and gene flow among experimental populations of the Texas gourd (Cucurbita texana) and cultivars of Cucurbita pepo. While flowering patterns and pollinator movement tended to maximize self-pollination and local gene exchange, movement of effective pollen exceeded 1,300 m. This movement, mediated by the solitary bee Xenoglossa strenua and monitored by tracking allozyme variants, produced interspecific hybrids in 5% of the progeny from experimental plants. Interspecific gene exchange occurred in either direction with either species serving as staminate or pistillate parent. No obvious constraints to gene flow among plants representing C. texana and distinctive cultivars (vars. ovifera, medullosa, melopepo) of C. pepo were detected. Genetic exchange among different species and cultivars is enhanced by the foraging behavior of Xenoglossa. Multiple visits to either staminate (pollen carryover) or pistillate (multiple pollinations) flowers often result in the deposition of mixed pollen on receptive stigmas. The wild type (C. texana) can donate and receive effective pollen when growing under both weedy and natural conditions. The observed lack of interspecific reproductive isolation supports treatment of cultivars and wild types as a single species and, in conjunction with available data concerning temporal/geographical relationships among bees, squash, gourds, and humans in eastern North America, suggests the possibility of long-term genetic interaction between wild types and domesticates.     

Quality of a stress-sensitive Cucurbita pepo L. pollen

The quality of Cucurbita pepo L. pollen was studied using field pollinations and the fluorochromatic-reaction test. The extreme sensitivity of this pollen to dehydration and ageing is demonstrated. Controlled stress applied to mature pollen leads to the development of seedless fruits. Molecular signals seem to be involved in the induction of this parthenocarpy. These results indicate the existence of distinct sequences involved in the completion of the fertilization program of pollen. With pollen altered by stress, the fertilization process may be stopped at different stages of its completion. We bring evidence that Cucurbita pepo plants have developed special adaptations in order to compensate for the poor viability of their pollen.Abbreviation FCR fluorochromatic reaction     

Individual quantitative rDNA variation in three species of the Cucurbitaceae family

Individual quantitative variation in rDNA content within three species of the Cucurbitaceae family has been studied by rRNA/DNA filter hybridization experiments. The results showed a 2.3-fold range of variation in the number of ribosomal cistrons per diploid cell in an Ecballium elaterium natural population. This range of variation is compared with the smaller range observed in three Cucumis sativus and in two Cucurbita pepo varieties obtained as F₁ hybrids between pure lines.This work was supported by CNR Contract No. 74/0267.     

Fruit size preference in the New Zealand pigeon (Hemiphaga novaeseelandiae)

Abstract We investigated whether the New Zealand pigeon Hemiphaga novaeseelandiae (Columbidae) exhibits size‐based preferences for fruits. We tested the hypothesis that in small‐fruited species, pigeons would prefer larger fruits, but in larger‐fruited species, this preference would reverse as the pigeons become increasingly limited by their gape size. We collected undispersed fruits and bird‐dispersed seeds of 10 plant species, some over several sites or years (13 datasets in total). We estimated the fruit size of dispersed seeds by fitting regressions of fruit diameter to seed diameter in intact fruits. We were able to predict fruit diameter from seed diameter in 12 of the 13 populations, although the relationship was stronger in single‐seeded species than in multi‐seeded species. Seven of the 12 populations tested showed a significant difference in seed diameter among undispersed and dispersed seeds. However, our results showed no consistent pattern in fruit size preference by the New Zealand pigeon and did not support our hypothesis. The large‐bodied New Zealand pigeon is generally not gape limited and fruit size preferences appear to be independent of mean fruit size.