Franklin W. Martin

The edible species ofPassiflora

Of the 400 known species of Passiflora, about 50 or 60 bear edible fruits. Probably all of these are indigenous to the American tropics. Although a few species have been introduced in tropical and subtropical regions and have become the basis for local industries, the majority of the edible passion fruits are unknown outside of the limited areas where they grow wild or are sometimes cultivated. Without doubt the littleknown passion fruits could contribute valuable germ plasm to the better known species, including genes for disease resistance, climatic tolerance, yield, and flavor. Because a major use of passion fruit is in the flavoring of juices and beverages, one might expect valuable progress to result from the hybridization of these highly aromatic and yet diverse species. The passion fruits of commerce are limited in number of species. In Hawaii P. edulis Sims f. flavicarpa Degener, the yellow passion fruit, is the basis of the entire passion fruit juice industry (Hawaii Agr. Exp. Sta., 1956). In Australia, Ceylon, and India, however, P. edulis Sims, the purple passion fruit, is most exploited (Pruthi, 1963). In Australia, both the yellow and the purple forms are grown, but the former is generally used as grafting rootstock for the latter (Cox and Kiely, 1961). In South America, other species are presently of more importance. P. ligularis Juss. and P. mollissima Bailey are frequently found in native markets. P. mollissima (HBK.) Bailey is confined to high altitudes. Finally, P. quadrangularis L., a melon-like fruit, has been widely disseminated throughout the tropics and is sometimes produced commercially on a small scale. Other passion fruits mentioned in the article are seldom seen except

Variation in Okra

SummaryA study of the variation of 29 characteristics of 585 varieties or seedlings of okra revealed that 17 West African varieties could be distinguished from all others on the basis of 5 discriminating characteristics. In addition, seedlings of the 3rd outcrossing generation of a population differed from a varietal collection in several characteristics, the most important of which were more seeds per pod and more pods per plant. This is believed to be the result of mass-selection. Country groups differed significantly in characteristics but these differences are believed to be due to small sample size. No such distinguishing characteristics were evident among country groups represented by large numbers of varieties.

Incompatibility in the Sweet Potato. A Review

Self-incompatibility (SI) is but one of the outerossing mechanisms extant in flowering plants that lead to a high level of heterozygosity in a population and to a genetical architecture based on homeostasis and hybrid vigor. But in contrast to other such systems, SI rigidly impedes self-pollination, which is desirable in breeding schemes for the rapid fixation of inherited characteristics as well as the testing of progeny and the derivation of inbred lines. SI may also be a barrier between plants of similar S (incompatibility) alleles, preventing exchange between them of desirable genes. Finally, SI may act as a unilateral barrier to crosses between self-incompatible and self-fertile individuals or species. In these respects, SI constitutes a nuisance and a problem to the plant breeder. Occasionally, SI may be an aid to the plant breeder. Self-incompatible plants may be crosspollinated with emasculation. Two self-incompatible varieties may be interplanted and permitted to cross through natural vectors. Yet, it is doubtful if these occasional advantages outweigh the inconveniences of incompatiblity. As an element of the breeding system, the type of incompatibility must be taken into account in the breeding of a crop planit. The type of SI may influence the crossing procedures used, the manner of selection of parents, and even the breeding goals. In some cases, the incompatibility may be avoided or bred out of a variety. In most crops, knowledge of the incompatibility system will spur breeding progress. The incompatibility system in the sweet potato (Ipomoea batatas Poir) has not yet been worked out in detail. Nevertheless, in widely scattered places in the biological literature, some of the facts concerning SI in

The species ofDioscorea containing sapogenin

Diosgenin, the sapogenin most widely used in the synthesis of steroidal drugs, was first discovered in 1936 by Fujii and Matsukawa. That discovery lay dormant for some years, however, until Marker and his associates (about 1943) revealed the potential use of plant sapogenins for the synthesis of cortisone and other drugs. After World War II, the growing need for steroidal drugs and the high cost of obtaining them from animal sources led to a widespread search for plant sources of steroidal sapogenins. That search has been ably documented by Correll et al. (11). The major program of the United States Department of Agriculture stimulated scores of other expeditions and screening programs of smaller scope among both public and private institutions. These continue today.

Post-pollen-germination barriers to seed set in sweet-potato

Three sweet-potato crossing combinations selected for good pollen germination were characterized by a moderate to high amount of failure of tubes to pass from stigma to style. The number of tubes penetrating the style was about 6 times the number of seeds produced. Ovules of compatibly pollinated flowers were divided into two classes, by size. Larger (probably fertilized) ovules matured into seeds, whereas smaller (probably unfertilized ovules) dried into scales. Besides the incompatibility barrier in sweet potato, which inhibits pollen-germination, a physiological or mechanical barrier between stigma and style is hypothesized. Pollen tube growth is not appreciably inhibited within the style. A third barrier between stylar penetration and mature seed development is postulated but not identified. However, the mechanism does not appear to be due to embryo abortion. Seed abortion leads to small, weak and inviable seeds, and thus represents a further reproductive loss.

Subspecific grouping of eggplant cultivars

SummaryEggplant cultivars from a world collection were classified into 11 groups by 18 characteristics using numerical taxonomic methods. Distinguishing characteristics of groups were identified on the basis of extreme means, and a key to the groups, based first on characteristics of the foliage, was devised. Some of the groups were also characterized by specific geographical origins. When eggplants were classified by geographical origin, however, less cohesive groups than those above were formed, but certain characteristics could be associated with orgins of eggplants. Thus, variation in this large eggplant sample is not distributed at random.

Barriers to the hybridization of Passiflora species

SummaryTo avoid compatibility barriers among species of passion fruit that do not normally set fruit, hormones were applied to the stigma following cross pollination. In other cases, two of the three stigmas were cross pollinated, and one was self-pollinated. With such treatments, abscission of the flower was often delayed. and seeds were produced. Seeds were often aborted at an early stage or failed to germinate. Seven new hybrid combinations were produced.

A WildIpomoea Species Closely Related to the Sweet Potato

In a brilliant study of certain species of Ipomoea closely related to the sweet potato Ipomoea batatas (L.) Lamn., Nishiyama (1971) claims not only to have found the primitive wild type of 90 chromosomes from which the sweet potato originated, but also to have resynthesized the wild type from a diploid and a tetraploid species. In contrast, in a very careful study of many of the diploid and tetraploid relatives of the sweet potato, Martin and Jones (1972) point out that none of the species so far found resembles the sweet potato enough to be its ancestor. They hypothesize that the described diploid species are closely related to each other, but that the tetraploid species show no close resemblances to each other, to the diploids, or to the sweet potato. Nishiyamas (1971) hypothesis is that the tetraploid progenitor of sweet potato is I. littoralis Blume, a species that when grown in Mayaguez, Puerto Rico, proved to be equal to what Martin and Jones (1972) have called I. gracilis R. Br. Matuda (1963) and van Oostroom (1953) consider I. littoralis to be a synonym for L gracilis. As they point out, the species has forms with cordate leaves as well as with lobed leaves. Nevertheless, Nishiyama apparently recognizes other differences, because he treats L littoralis and L gracilis as separate species (1971).

First-generation hybrids of edible passion fruit species

SummaryThrough cross-pollinations among 42 combinations of 7 passion fruit species, 6 new hybrids were produced. Most of the hybrids were vigorous, but they varied in tendency to flower. Although intermediate to parent species in characteristics of the foliage, flowers, and fruits, unique characteristics were often evident. The hybrids varied in degree of sterility of pollen, and in success of selfing and backcrossing. Pollen was often aborted, but fertility as female was frequently sufficient to permit some seed production. The fruit varied in quality, but one combination, Passiflora edulis f. flavicarpa x P. alata, produced a fruit superior to those of the parent species. The possibility of cross-breeding to improve edible passion fruit species has thus been demonstrated.

Sterility in some species related to the sweet potato

SummaryThe kinds and sites of sterility and inviability were noted in induced tetraploids of threeIpomoea species, and of hybrids ofIpomoea lacunosa withI. trichocarpa. Tetraploids were somewhat less fertile than diploids, but seeds were normal appearing and ususally viable. Hybrids were much less fertile. Hybrid sterility occurred as pollen abortion, pollen germination failure, and in failure of pollen tube growth. Small and underdeveloped seeds failed to germinate. The sterility of hybrids (but not of tetraploids) is thus very similar to that of the hexaploid sweet potato. Sterility suggests developmental inbalance, which is probably due to genic and perhaps minor chromosomal differences among the parent species of the sweet potato. Hybrid sterility of the sweet potato may have been fixed by polyploidy, and thus may be impossible to eliminate.