Quantitative Assessment of Some Factors Limiting Seed Set in Buckwheat

Abstract

estimate of fitness, for example, seed set. Likewise, the theory of reproductive strategies of plants has been in-A healthy buckwheat (Fagopyrum esculentum Moench) plant profluenced by our ability to determine the mechanisms by duces numerous flowers but few seeds. The objective of this study was to investigate mechanisms responsible for the low frequency of which selection may occur. seed set. Newly open and receptive flowers were pollinated at weekly Reduced seed number can be caused by: (i) insuffiintervals from 4 to 12 wk after seeding (WAS) on selected racemes cient pollination, (ii) sexual selection of male and female of greenhouse-grown plants. Flower number, seed set, abortion, and gametophytes, and (iii) resource limitation of the materanatomical observations of egg sacs and proembryos were analyzed. nal plant (Bawa and Webb, 1984). The male component Although flowers formed continuously for 7 wk, the period of maxiof fitness has been assessed in Campsis radicans (Bertin, mum seed set under controlled conditions was brief (1-2 wk). Compe-1982), Calathea ovandensis (Horvitz and Schemske, 1988), tition within the same nutritional unit (raceme) did not account for Cassia fasiculata (Lee and Bazzaz, 1982), Agave mckellow average seed set per raceme. Neither the number of flowers nor veyana (Sutherland and Delph, 1984), and Lithopserfrequency of seed set was decreased when developing seeds were on mum caroliniense (Weller, 1980). In some cases the evithe same raceme. Abortion (≈10%) was not a major factor limiting seed set. Eighty percent of the flowers failed to initiate seeds even dence indicates that excess flowers contribute to male under controlled growing conditions when hand pollinated. Approxi-fitness by acting as pollen donors (Agave), while in mately 20% of megagametophytes appeared to be defective at antheother cases (Cassia, Lithospermum, Calathea, Campsis) sis. The proportion of ovules containing a proembryo at 24 h after it does not. Sutherland (1987) pooled published obserpollination (HAP) paralleled the proportion initiating seeds, indicatvations of 445 species to test hypotheses related to male ing that fertilization is a limiting process. Pollen tube remnants were fitness. He concluded that excess flowers that fail to observed near the micropyle in 65% of the unfertilized ovules at 24 form mature fruits do not contribute to female fitness HAP. Lack of fertilization accounts for most of the reduction in seed(fruit or seed set) because they abort regardless of their set, appears to be caused by failure of the pollen tube to grow into pollination history. They may act as pollen donors, howthe micropyle, and increases with plant age at pollination. Flowers ever, and thus contribute to male fitness. Conditions for that form late in the plant cycle contribute little to seed set and may be ignored in yield management decisions.

Morph Differences and Honeybee Morph Preference in the Distylous Species Fagopyrum esculentum Moench

“…Indeed, it could be that not all ovules produced were viable and therefore capable of being cross-fertilized. According to Taylor and Obendorf (2001), ca. 20% of megagametophytes appeared to be defective in buckwheat at anthesis, and fertilization is a limiting process.…”

“…Low seed set constitutes a major constraint to buckwheat culture in the main growing countries. The causes of this reduced fertility remain essentially unknown, although environmental stresses (high temperatures, water stress), resource limitations, inadequate pollination, and fertilization problems (defective reproductive organs, failure of fertilization due to self-incompatibility or seed abortion) have been investigated (Marshall and Pomeranz 1982;Bjö rkman 1995b;Goodman et al 2001;Taylor and Obendorf 2001;Halbrecq et al 2005).…”

Osmotic stress at seedling stage impairs reproductive development in buckwheat (Fagopyrum esculentum)

“…However, despite obvious nutritional qualities and its ability to treat or prevent diseases like diabetes, hypertension and cancers (Campbell 1997, Hagels 1999, Holasova et al 2002, Kreft 2001, Tahir and Farooq 1988), its production in the main growing countries strongly declined during the last decades. There are several reasons why buckwheat has fallen out of favour including (1) its failure to benefit from modern agriculture improvements (Adachi 1990, Marshall and Pomeranz 1982); (2) its erratic yields linked to an indeterminate growth habit and the occurrence of defective reproductive organs (Funatsuki et al 2000, Guan and Adachi 1992, Taylor and Obendorf 2001) and (3) its sensitivity to drought (Delpérée et al 2003, Marshall and Pomeranz 1982, Slawinska and Obendorf 2001). In addition, buckwheat is a hermaphroditic self‐incompatible species producing distylous flowers (pin‐ and thrum‐type), which makes breeding programmes difficult.…”

Pollen–pistil interaction, pistil histology and seed production in A×B grain sorghum crosses under chilling field temperatures

“…The proportion of fertilized pistils (FP), i.e. with a widened ovary (Taylor & Obendorf 2001), was then calculated. The remaining branches in the panicle were left untouched until harvest, to measure seed yield and its components.…”

“…23 and 0 . 87) are probably due to a combination of factors : the sample size (Marshall & Diggle 2001), the sigmoid shape of the accumulated germination curve of pollen (Sun et al 1991) ; the lower number of pollen tubes than the pollen grains initially germinated (Hodnett et al 2005;Price et al 2006) ; the low fertilization efficiency (many pollen grains germinate but do not fertilize) (Taylor & Obendorf 2001) ; and the interactions between the gametophyte (pollen and embryo sac) and sporophyte (ovary) tissues (Weterings & Russell 2004). The proportion of pollen tubes in the stigma compared to pollen grains initially adhered ranged from 0 .…”