Peter D. Ascher

Invasiveness in wetland plants in temperate North America.

The spread of invasive taxa, includingLythrum salicaria, Typha × glauca, Myriophyllum spicatum, Phalaris arundinacea, andPhragmites australis, has dramatically changed the vegetation of many wetlands of North America. Three theories have been advanced to explain the nature of plant invasiveness. Aggressive growth during geographic expansion could result because 1) growth is more favorable under new environmental conditions than those of resident locales (environmental constraints hypothesis); 2) herbivores may be absent in the new locale, resulting in selection of genotypes with improved competitive ability and reduced allocation to herbivore defenses (evolution of increased competitive ability hypothesis); and 3) interspecific hybridization occurred between a new taxon and one existing in an area, resulting in novel phenotypes with selective advantages in disturbed sites or phenotypes that can grow under conditions not favorable for either parent (introgression/hybrid speciation hypothesis). A review of published literature found few studies that compare the growth and dynamics of invasive populations in their new range versus those in historic ranges. However, there is evidence that hydrologic alterations could facilitate invasions byTypha × glauca andPhalaris arundinacea and that increased salinity promoted spread ofTypha angustifolia (parental taxon) andPhlaris arundinacea and that increased salinity promoted spread ofTypha angustifolia (parental taxon) andPhragmites australis. The potential for reduced herbivory causing aggressive growth is greatest forLythrum salicaria. Introgressive hybridization is potentially a cause of invasiveness for all five species but has been established only forTypha × glauca andLythrum salicaria.

Fertile, intermediate hybrids between Phaseolus vulgaris and P. acutifolius from congruity backcrossing

SummaryRecurrent or introgressive backcrossing of Phaseolus vulgaris — P. acutifolius hybrids with either P. vulgaris or P. acutifolius increased fertility, as measured by pollen stainability and seed per pod from non-manipulated flowers, while invariably resulting in loss of traits from the non-recurrent parent. When hybrids were backcrossed with each of the parent species in alternate generations (congruity backcrossing), fertility decreased in early generations but gradually increased in later generations. By the fourth or fifth generation, congruity-backcross hybrids produced numbers of seeds per pod from non-manipulated flowers comparable to those of parent species, although the percent of stainable pollen tended to be lower. Congruity-backcross hybrids were intermediate to parent species when pedigrees contained equal representation of parents but favored the majority parent when pedigrees were unbalanced. Individuals exhibiting symptoms of developmental incongruity, such as abnormal leaflet number, foliar variagation, or unusual growth patterns, occurred in each generation. However, completely new characteristics appeared after the second backcross generation, presumably due to recombination. Backcrossing to both parent species in alternate generation reversed incongruity, allowing selection for fertility without loss of traits from one of the parent species.

Genetic studies of self incompatibility in the garden chrysanthemum, Chrysanthemum morifolium ramat

SummarySelf incompatibility was investigated in the hexaploid garden chrysanthemum, a member of Compositae. Nine sibling clones selected from a highly compatible cross were all self incompatible. 14.8% of the crosses between these sibs in diallel were compatible, but one sib, 67-111-42, accounted for 10 of the 12 compatible crosses. 67-111-42 was also more compatible than the remaining 8 sibs in crosses to other closely related plants. Crosses of the 9 sibs to 12 unrelated tester clones indicated that none were male or female sterile. Inbreeding via pseudocompatibility was successful in increasing homozygosity at the S loci. The percentage of compatible crosses obtained in 3 sib diallels of I2 clones from crosses of 67-111-42I1 plants approached that of the original 9 × 9 diallel, but no one individual accounted for most of the compatible crosses. It was possible to separate the 9 sibs into 9 incompatibility patterns from the pollinations made in this study. The evidence suggests that the self-incompatibility reaction in the garden chrysanthemum is sporophytic and involves more than 1 locus.

Inheritance of the photoperiodically induced cold acclimation response in Cornus sericea L., red-osier dogwood

SummaryCold acclimation responses of latitudinal ecotypes of Cornus sericea L. (C. stolonifera Michx.) and F1, F2 and BC1 hybrid progenies were measured under natural photoperiod conditions in St. Paul, MN and artificially shortened photoperiods in the glass-house. The 65 °N and 62 °N ecotypes (Alaska and Northwest Territories, respectively) were characterized by a short night length for hardiness induction, the 42 °N ecotype (Utah A and B) by a long night length for hardiness induction, while the F1 was intermediate to the parents. Results from reciprocal crosses indicated there was no significant unilateral maternal influence on cold acclimation. Acclimation responses of the F2 were highly variable but generally ranged between the parental extremes. However, three individuals from the 42 ° × 62 °N crosses exhibited greater cold resistance than the northern parent on two successive freezing test dates. F2 plants were also found with less freezing resistance than the southern parent. Backcrosses to the southern parent produced progeny with acclimation patterns resembling that of the southern parent and were significantly less hardy than the F2 in early freezing tests.

The inheritance of pseudo-self-compatibility (PSC) in Nemesia strumosa Benth

SummaryPseudo-self-compatibility (PSC) in Nemesia strumosa was determined by recessive modifying genes which interferred with the normal stylar incompatibility reaction. The PSC levels ranged from none or low to amounts resembling full self-compatibility. PSC within a progeny could be maintained at low or high levels by selecting parents either high or low in PSC. Pollen from plants of any PSC level failed to produce seed when placed on other incompatible styles bearing the same S alleles.

Self compatibility in garden Chrysanthemum: occurrence, inheritance and breeding potential

SummarySelf compatibility (SC), which was found to occur only rarely in the normally self-incompatible (SI) hexaploid garden chrysanthemum, Chrysanthemum morifolium Ramat., was studied by making a series of self and cross pollinations in progenies of 3 different SC sources. SC was transmitted without exception in 15 F1 progenies from crosses between SC and SI plants. No maternal effects were noted in 10 F1. progenies from reciprocal crosses between SC and SI plants. Selfing or intercrossing of SC plants did not produce any large, uniformly SC progenies. Initial intercrosses between SC and SI plants suggested that SC might be controlled by a single dominant factor. Further crosses suggested that the inheritance of SC was more complex and could be associated with more than 1 gene or be modified by other genes such as the S-genes. Seed yield following self pollination in some progenies gave evidence of a clear separation into SC and SI classes while in other progenies the separation was not so distinct. The condition of pseudoself-compatibility was evident in progenies derived from selfing SC plants or crossing between SC plants. SC was used to produce large quantities of inbred seed which is now available for producing both I1 and I2 generations. By using SC parents, the combined self and cross compatibility was increased as compared to compatibility in progenies derived from SI-SI matings.

Multigenic self incompatibility in hexaploid Chrysanthemum

SummaryEleven garden chrysanthemum siblings obtained through two generations of single-plant selfpollination were selfed and crossed in a complete diallel. Outcrosses to unrelated individuals were performed to test for male and female fertility. Since eleven crossing patterns were found inthe diallel, at least three genes must be assumed. Our data suggest independent gene action with intragenic dominance. One inbred, 77-AM3-3, expressed a high level of pseudo-self-compatibility (PSC) by giving some very low cross seed sets along with high self seed set. This inbred also exhibited variable PSC from season to season.

Special Stylar Property Required for Compatible Pollen-Tube Growth in Lilium longiflorum Thunb.

Lilium longiflorum (Easter lily) styles capable of supporting compatible pollen-tube growth possess a special property. Compatible pollination of styles lacking this property results in tube growth indistinguishable from that of incompatible pollen tubes in normal styles. This property is not present in L. longiflorum styles aged 6-8 days from anthesis at room temperature or more than 12 days at 4-7 C. It can be removed from Easter lily styles aged at room temperature 5-6 days or at 4-7 C for 7-10 days by immersing them in 50 C water for 6 min; from styles aged 14 days from anthesis at 4-7 C by flushing the stylar canal with 10 drops of distilled water; from styles immersed in 50 C water the day after anthesis by flushing the stylar canal; and from styles aged 1 day from anthesis at room temperature by immersing them in 50 C water for 8 min. The capacity to support compatible pollen-tube growth was not restored in heat-treated (immersed in 50 C water for 6 min), flushed styles by prepollination injection of stigmatic exudate. Similarly, prepollination injection of the material collected by air flushing heat-treated styles had no effect on pollen-tube growth in styles unable to support compatible tube growth because of aging at 4-7 C.

S allele discrimination in styles of Petunia hybrida bearing stylar-conditioned pseudo-self-compatibility.

SummaryA cross between a 0% pseudo-self-compatible (PSC) plant (S3.3) and a 100% PSC plant (S1.1) yielded an F1 population which, when selfed, produced a high mean seed set which was not significantly different than that produced when the F1 was backcross pollinated by the 100% PSC parent. Backcross pollinating the F1 with the 0% PSC parent yielded no seed. No S3.3 plants were recovered in the F2 populations, indicating that pollen tubes containing the S3 allele were inhibited during pollen tube growth of the selfed F1 plants. Apparently stylar-conditioned PSC does not remove all discriminatory power from these petunia styles. Crossing the F1 (S1.3) with an self-incompatible (SI) plant (S2.2) produced plants which were used for computation of a standard linkage test. An approximate map distance of 28 units was found between the S specificity locus and the major gene(s) which influenced its expression. Other generalized PSC modifying genes apparantly were not linked with the S locus.

Congruity backcrossing as a means of creating genetic variability in self pollinated crops: Seed morphology of Phaseolus vulgaris L. and P.acutifolius A.Gray hybrids

SummarySeeds of early generations of three reciprocal congruity-backcross (CBC) pedigrees, developed by backcrossing Phaseolus vulgaris-P. acutifolius hybrids to each of the parent species in alternate generations, exhibited a preponderance of traits (size, shape, color, and pattern) of the cytoplasmic parent. The large size of ‘Red Cloud’ (V1), the P. vulgaris parent common to all of the pedigrees, dominated pedigrees with V1 as the cytoplasmic parent, while the small size and rounded or square shapes of the tepary parents, wild P. acutifolius var. acutifolius PI 263590 or G400445 (A19), wild P. acutifolius var. latifolius PI 406622 (A10), or cultivated P. acutifolius var. latifolius ‘Serowi’ PI 319443 (A9), were the majority phenotypes when P. acutifolius was the cytoplasmic parent. Continuing through the second cycle of CBC, that is the second backcross with each of the parent species or the fourth backcross, began an amelioration of the apparent cytoplasmic effect on gene expression, as reciprocal pedigrees became more alike, usually with intermediate expression of parental traits or the appearance of new traits. The large seed size of V1 was recovered in hybrids with P. acutifolius cytoplasm and the kidney shape of V1 became rare in hybrids with P. vulgaris cytoplasm. Although the tepary-bean parents represented two subspecies and both cultivated and wild P. acutifolius, the three sets of reciprocal-hybrid pedigrees with P. vulgaris ‘Red Cloud’ are surprisingly similar. It may be that the ‘exotic’ parent used to develop a CBC pedigree should be selected more for combining ability in the interspecific cross than for specific economic traits. While the number of generations (six or more) required to produce fertile, intermediate CBC hybrids (that did not require embryo rescue) may preclude routine use of this method by practical plant breeders, the crossability of advanced hybrids with both parental species and the amount of variability apparent in advanced-hybrids progenies suggests that CBC would be valuable for maintaining ‘exotic’ germplasm in immediately useful forms.