Role of the male parent in crosses involving apomictic Rubus species

Abstract

Received i 2.iii.591. PSEUDOGAMY IN APOMICTIC RUBUS THE polyploid species of Rubus which comprise most of the European blackberry population are apomictic, in contrast to the few diploid species, such as the two primary European species R. u1mfolius and R.tomentosus. It is essential for fruit setting in these pseudogamous apomicts that they must be pollinated with viable pollen (Darrow and Waldo, 1933;Crane and Thomas, 1940; Gustafsson, i943).Focke used the term pseudogamy in i 88i for "parthenogenetic development where pollen-tubes effect the embryo-formation without any previous fusion of egg and sperm nucleus" (Gustafsson's translation), and it will be used in this sense in this paper. In his review of pseudogamy in apomictic Rubus species, Gustafsson (I93) has stated that " pseudogamy" consists of an act of "partial fertilisation ", that is fertilisation of the endosperm nucleus but not of the eggs, and is not due solely to hormone activity. That the latter part of this statement is probably correct is supported by the failure in the present study to obtain stimulation in R. laciniatus after brushing the ripe stigmas with freshly prepared concentrated aqueous extract of its pollen. Pollen from the related genus Rosa is ineffectual. Those pollinations of pseudogamous facultative apomicts which result in more or less maternal-like seedlings, and with the production of only an occasional sexual hybrid when the pollen from another species is used, are given in inverted commas in this paper. A proposed life-cycle for the apomictic tetraploid species R. laciniatus is given in fig. i, and is based on the cytological observations of Kerr This cycle is concerned only with the production of the tetraploid apomictic seedlings. The chief difference between sexual and pseudogamous Rubus species lies in the establishment of the megagametophyte, usually only one gametophyte develops in the sexual whereas from two to four are formed in the pseudogamous species, but the supranumerary gametophytes disintegrate as development progresses.The relative frequency of diplospory and apospory is a specific characteristic, according to Christen (1950).Two series of investigations have been made in an attempt to explore further the genetical and evolutionary properties of pseudogamy in Rubus. The first study was initiated to determine whether

The inheritance of thornlessness from tissue culture-derived ‘Thornless evergreen’ blackberry

“…Many of the thorny and thornless (respectively) seedlings were apomicts. Apomixis, a phenomenon whereby seeds contain embryos of maternal, not sexual, origin, is very common among Rubus species (CRANE 1940;THOMAS, 1940;HASKELL, 1960). Using methods similar to those of HAS- KELL (1960), presumed thorny segregants from TE x TE, often could be differentiated from apomicts by their leaf morphology.…”

“…Using methods similar to those of HAS- KELL (1960), presumed thorny segregants from TE x TE, often could be differentiated from apomicts by their leaf morphology. Apomicts had lacinate leaves, a character that is reported to be recessive to the normal-leaf type (HASKELL, 1960). Those seedlings that were clearly different from the parental apomictic type were presumed to be sexual segregants.…”

“…When the plants were large enough, their leaf shape (normal or lacinate), growth habit (full sized or dwarf), thorn status (thorny of thronless) and petiole condition (straight or bent) was recorded. Prior to statistical analysis, presumed apomicts were separated from sexually-derived seedlings by leaf morphology and prickle colour, using the methods described by HASKELL( 1960). Since TE is a tetraploid and the mutant thornless character has been expressed repeatedly in the field (DARROW, 1931(DARROW, , 1937, it is reasonable to assume that the gene(s) for thornlessness is (are) dominant to the thorny alleles.…”

Evolution of gametophytic apomixis in flowering plants: an alternative model from Maloid Rosaceae

“…One possibility involves what Haskell (1960) has termed ''pseudogamous heterosis'', i.e. heterosis effects due to an ''out-crossed'' endosperm that can improve seedling vigor.…”

Temporal and spatial patterns in the production of pollen, ovules and seeds in pseudogamous blackberries (Rubus subgenus Rubus)

“…However, the primary flowers sometimes show a slightly greater number of ovules. Sinee inter-plant pollination in Rubus is more common in primaries (Haskell 1955), large numbers of ovules could be an adaptation that increases genetie variation in the offspring by intraspecifie cross-pollination. Apart from possibly being of importance to the sexual ancestors, the tetraploids eould also benefit since they seem to produee e. 20-30% sexual offspring (Nybom 1988).…”