T. D. Hong

Basic and Applied Aspects of Seed Biology

The relevance of seed science especially that concerned with viability and dormancy to solving practical problems concerned with plant breeding and genetic conservation is discussed. It is unfortunate that, in spite of considerable effort and voluminous literature, we are still uncertain about the physiological and molecular mechanisms involved in these processes. But take heart, for sometimes such knowledge is not necessary, and may not even be helpful for predicting what will happen under different circumstances to populations or organisms such as seeds. Solutions to practical problems, however, often demand quantitative predictions which are valid in a wide range of circumstances; and such solutions are sometimes achievable. Nevertheless, the possibilities of productive interactions between those concerned with fundamental problems and those concerned with practical problems are increasing, and this series of International Workshops provides important opportunities to encourage this symbiosis.

Effect of storage temperature and moisture on the germination of papaya seeds

Seeds of papaya ( Carica papaya L.) stored for 12 months at 15°C with 7.9–9.4% moisture content maintained their original germination. In contrast, many seeds stored cooler or drier lost viability, the losses occurring more rapidly at −20°C than at either 0°C or 15°C. The results are not compatible with the definitions of either orthodox or recalcitrant seed storage behaviour.

The effect of storage environment on the longevity of conidia of Beauveria bassiana

The effect of air-dry storage environment on the longevity of conidia from seven isolates of Beauveria bassiana produced at different times and locations was determined by estimating the parameters of a viability equation. Conidia were stored hermetically at six to 11 moisture contents between 2.3 and 32.0% with one (50 ± 0.5 °C) to five constant temperatures (10, 20, 30, 40 and 50 ± 0.5°) for various periods up to 372 d and then tested for viability. All isolates behaved similarly (P > 0.25) in terms of the relative effect of moisture content (Cw) and temperature (CH and CQ) on conidial longevity; common values were Cw = 3.05 (SE = 0.07), CH = 0.0293 (SE = 0.0078), and CQ = 0.00081 (SE = 0.00011). Estimates of the low-moisture-content limit to the negative logarithmic relation between conidial moisture content and longevity were 4.6 and 5.0% at 50° and 40°, respectively, for isolate I98–1140ss, and 5.2 and 5.1% moisture content, respectively, for isolate I97–1111. Absolute longevity (KE) varied considerably (P

Development of desiccation tolerance in Norway maple ( Acer platanoides L.) seeds during maturation drying

Norway maple ( Acer platanoides L.) seeds were harvested at different stages of seed development and maturation in 1989–91. As maturation drying progressed, the seed populations showed increasing desiccation tolerance: at 67–69% moisture content, no seeds survived desiccation below 10% moisture content; maturation drying to 55–57% moisture content (values corresponding with the end of the seed-filling phase) improved desiccation tolerance, but nevertheless most seeds were unable to withstand desiccation to 5–7% moisture content; further maturation drying to 27–28% moisture content enabled the seeds to survive considerable desiccation, no loss in viability occurring in seeds dried to 3% moisture content. This considerable improvement in desiccation tolerance after the end of the seed-filling phase was correlated ( P

The effects of duration of development and drying regime on the longevity of conidia of Metarhizium flavoviride

Conidia of the entomopathogenic Metarhizium flavoviride were harvested 8, 10, 12 or 15 d after inoculation at 25 °C and then (as conidiated rice) dried rapidly (10–12% r.h. and 17–20° for 17 h to about 15–22% moisture content) or slowly (50–60% r.h. and 27° for 5 d to about 27–32% moisture content initially). The subsequent survival of these conidia in air-dry storage at 50° with 8 1% moisture content was then assessed. Conidia longevity (assessed by the duration of storage until conidia viability was reduced to 50%, p 50 ) was maximal when conidia were harvested 10 d after inoculation, and was much greater following slow rather than rapid drying. The substantial beneficial effect of slow desiccation to subsequent conidia survival is consistent with that detected in other propagules in anhydrous biology, and is also of considerable practical utility for the biological control of insects by entomopathogenic fungi.

Relative humidity, temperature, and the equilibrium moisture content of conidia of Beauveria bassiana (Balsamo) Vuillemin: a quantitative approach

Abstract Isotherms for conidia of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin were determined at nine constant temperatures between 10 and 50°C using saturated salt solutions. Seven different mathematical models were compared to quantify the effect of temperature and relative humidity on the equilibrium moisture content of conidia. A seven-term polynomial regression model with moisture content expressed on the fresh weight basis ( R 2 =0.998, 103 df) was the best and provided no systematic deviation between observed and fitted moisture contents. This model will be a component of a geographical information system to determine the potential utility of B. bassiana for the control of grain borers in grain stores throughout the tropics.

Recovery of nodulated cowpea plants (Vigna unguiculata (L.) Walp.) from waterlogging during vegetative growth

SummaryWaterlogging pot-grown cowpea plants for eight days (24–32 from sowing) during the period of rapid vegetative growth when symbiotic nitrogen fixation rates are also increasing at maximum rate had effects on anatomical, morphological and physiological attributes of the legume system viz reduced nodule production and increased nodule cortication, stimulated adventitious root formation at, or near, the water table but killed older submerged roots and nodules, caused the main stem to become hypertrophic just above the water line, accelerated senescence of the lowermost leaves and delayed branch formation. After re-draining the rooting medium nodule growth and symbiotic fixation activity occurred at the expense of rapid recovery by the host plant. The physiological basis for these findings in relation to identifying cowpea cultivars more tolerant of waterlogged soils is discussed.

Onset of germinability, desiccation tolerance and hardseededness in developing seeds of Peltophorum pterocarpum (DC) K. Heyne (Caesalpinioideae)

In the hot and dry conditions in which seeds of the tree legume Peltophorum pterocarpum develop and mature in Vietnam, seed moisture content declined rapidly on the mother plant from 87% at 42 d after flowering (DAF) to 15% at 70 DAF. Dry weight of the pods attained a maximum value at about 42 DAF, but seed mass maturity (i.e. the end of the seed-filling phase) occurred at about 62 DAF, at which time seed moisture content was about 45-48%. The onset of the ability of freshly collected seeds to germinate (in 63-d tests at 28-34degreesC) occurred at 42 DAF, i.e. about 20 d before mass maturity. Full germination (98%) was attained at 70 DAF, i.e. at about 8 d after mass maturity. Thereafter, germination of fresh seeds declined, due to the imposition of a hard seed coat. Tolerance of desiccation to 10% moisture content was first detected at 56 DAF and was complete within the seed population by 84 DAF, i.e. about 22 d after mass maturity. Hardseededness began to be induced when seeds were dried to about 15% moisture content and below, with a negative logarithmic relation between hardseededness and moisture content below this value.