A. Qi

Characterization of Photothermal Flowering Responses in Maturity Isolines of Soyabean [Glycine max (L.) Merrill] cv. Clark

All eight isolines of three maturity genes (E(1)/e(1), E(2)/e(2), and E(3)/e(3)) of soyabean [Glycine max (L.) Merrill] cv. Clark were grown in widely different combinations of photoperiod and temperature. Under the more inductive conditions, i.e. in a warm mean temperature (30 degrees C) when daylengths were less than the critical value (i.e. less than about 13 h), the isolines flowered at similar times (23-24 d). The responses of all isolines to temperature were also similar, if not identical. Increase in daylength above the critical photoperiod progressively delayed flowering until the time taken to flower (f) reached a maximum at the ceiling photoperiod. The relations between the rate of progress towards flowering (1/f) and photoperiod (between the critical and ceiling values) were linear. The coefficient characterizing the slope of the response (photoperiod sensitivity) varied amongst the isolines. These responses could be grouped into three categories of increasing sensitivity: (1) least sensitive, e(1)e(2)e(3), e(1)E(2)e(3), e(1)e(2)E(3); (2) intermediate, E(1)e(2)e(3), e(1)E(2)E(3), and (3) most sensitive, E(1)E(2)e(3), E(1)e(2)E(3), E(1)E(2)E(3). Thus, in the Clark cultivar genetic background, E(1) induces greater photoperiod sensitivity but neither E(2) nor E(3) on their own have any effect. However, both E(2) and E(3) together induce photoperiod sensitivity comparable to that induced by E(1) alone. Furthermore, in addition to this epistasis, either E(2) or E(3) has considerable epistatic effect on E(1), further increasing photoperiod sensitivity. The effects of these genes and their epistasis were also reflected in the extent of the maximum delays to flowering which occur when the ceiling photoperiod is exceeded, and also possibly in earliness in circumstances when photoperiods were below the critical value.

Effects of temperature and photoperiod on phenology as a guide to the selection of annual legume cover and green manure crops for hillside farming systems

Abstract The effects of temperature and photoperiod on times from sowing to flowering and maturity in a range of multi-purpose leguminous cover crop species have been investigated in controlled environments in order to quantify the photothermal coefficients which determine their potential environmental adaptation. Six genotypes representing six tropical or subtropical species were grown in 12 environments comprising all combinations of mean diurnal temperatures of 17, 22 and 27°C and photoperiods of 11.5, 12.5, 13.5 and 14.5 h day −1 . Another six genotypes representing five temperate species were grown in nine environments comprising all combinations of 17, 22, and 27°C and photoperiods of 12.5, 13.5 and 14.5 h day −1 . For all tropical and subtropical species, the warmest temperature combined with the shortest photoperiod hastened flowering and fruit maturity. However, except for Lupinus mutabilis which was photoperiod-insensitive, all temperate species both flowered and matured sooner at the warmest temperatures combined with the longest photoperiod. These photothermal responses in phenological development were amenable to modelling. Times to flowering were satisfactorily described using a general triple plane rate model. Rates of progress from first flowering to first mature pod were also satisfactorily modelled using temperature alone as the independent variable. These photothermal and thermal relations have identified considerable inter-specific differences in phenological responses to environment. The relations can now be applied to reveal the relative suitabilities of these diverse species as potential cover crops across hillside environments throughout the tropics and subtropics.

Use of field observations to characterise genotypic flowering responses to photoperiod and temperature: a soyabean exemplar

Thirty-nine accessions of soyabean [Glycine max (L.) Merrill] and 1 of wild annual soyabean (Glycine soja L.) were sown at two sites in Taiwan in 1989 and 1990 and on six occasions during 1990 at one site in Queensland, Australia. On two of the occasions in Australia additional treatments extended natural daylengths by 0.5 h and 2 h. The number of days from sowing for the first flower to appear on 50% of the plants in each treatment was recorded (f), and from these values the rate of progress towards flowering (1/f) was related to temperature and photoperiod. In photoperiod-insensitive accessions it was confirmed that the rate is linearly related to temperature at least up to about 29°C. In photoperiod-sensitive genotypes this is also the case in shorter daylengths but when the critical photoperiod (Pc) is exceeded flowering is delayed. This delay increases with photoperiod until a ceiling photoperiod (Pce) is reached. Between Pc and Pce, 1/f is linearly related to both temperature (positive) and photoperiod (negative), but in photoperiods longer than Pce there is no further response to either factor. The resulting triple-intersecting-plane response surface can be defined by six genetically-determined coefficients, the values of which are environment-independent but predict time to flower in any environment, and thus quantify the genotype x environment interaction. By this means the field data were used to characterise the photothermal responses of all 40 accessions. The outcome of this characterisation in conjunction with an analysis of the world-wide range of photothermal environments in which soyabean crops are grown lead to the following conclusions: (1) photoperiod-insensitivity is essential in soyabean crops in temperate latitudes, but such genotypes flower too rapidly for satisfactory yields in the tropics; (2) photoperiod-sensitivity appears to be essential to delay flowering sufficiently to allow adequate biomass accumulation in the warm climates of the tropics; (3) contrary to a widely held view, some degree of photoperiod-sensitivity is also needed in the tropics if crop-duration homeostasis is required where there is variation in sowing dates (this is achieved through a photoperiod-controlled delay in flowering which counteracts the seasonal increase in temperature that is correlated with increase in day-length); and (4) a greater degree of photoperiod-sensitivity is necessary to provide maturity-date homeostasis for variable sowing dates — a valuable attribute in regions of uncertain rainfall. Since the triple-intersecting-plane response model used here also applies to other species, the use of field data to characterise the photothermal responses of other crops is discussed briefly.

Variation in the Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Development to Flowering Among Eight Maturity Isolines of Soyabean [Glycine max (L.) Merrill]

In soyabean [Glycine max (L.) Merrill] the period between sowing and flowering is comprised of three successive developmental phases--pre-inductive, inductive and post-inductive--in which the rate of development is affected, respectively, by temperature only, by photoperiod and temperature, and then again by temperature only. A reciprocal-transfer experiment (carried out at a mean temperature of 25 degrees C) in which cohorts of plants were transferred successively between short and long photoperiods and vice-versa showed that eight combinations of three pairs of maturity alleles (E(1)/e(1), E(2)/e(2), E(3)/e(3)) had their greatest effect on the duration of the inductive phase in long days. This phase was increased with the increasing photoperiod sensitivity induced by the different gene combinations, and ranged from about 27 to 54 d according to genotype. In a short day regime (11.5 h d(-1)), less than the critical photoperiod, the duration of the inductive phase was brief-requiring about 11 photoperiodic cycles in the less photoperiod-sensitive genotypes and only about seven cycles in the more sensitive ones. The maturity genes also affected the duration of the two photoperiod-insensitive phases; these durations were positively correlated with the photoperiod-sensitivity potential of the gene combinations. The largest effect was on the pre-inductive phase which varied from 3 to 11 d, while the post-inductive phase varied from about 13 to 18 d. As a consequence of these nonphotoperiodic effects of the maturity genes, even in the most inductive regimes (daylengths less than the critical photoperiod) the time taken to flower by the less photoperiod-sensitive combinations of maturity genes was somewhat less than in the more sensitive combinations-ranging from about 28 to 34 d. The genetic and practical implications of these findings are discussed.

Modelling the effects of temperature on the rates of seedling emergence and leaf appearance in legume cover crops

Simple models of the growth and development of legume cover crops in different environments may aid the selection of species and genotypes most suitable for particular farming systems. The effects of temperature and photoperiod on the daily rate of seedling emergence (1/t 50% ) and the rate of leaf appearance (leaves d⊃−1&/sup;) were quantified for 12 diverse legume cover crop species. Six tropical or subtropical species were grown in 12 combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (11.5, 12.5, 13.5 and 14.5 h d⊃−1&/sup;). Another six genotypes of temperate species were grown in nine combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (12.5, 13.5 and 14.5 h d⊃−1&/sup;). Durations from sowing to 50% seedling emergence (t 50% ) were recorded and the number of leaves on the main stem counted during early vegetative growth. Photoperiod did not affect either 1/t 50% or leaves d⊃−1&/sup;. However, the effects of temperature, photoperiod response group (short-day or long-day response), genotype or species and their interactions were all significant. An optimal temperature between 21.8 and 26.8 °C for leaves d⊃−1&/sup; was identified for Vicia sativa , Vicia dasycarpa and Lupinus mutabilis . Below the optimum temperature, 1/t 50% and leaves d⊃−1&/sup; were positive linear functions of temperature for all legume species except Vicia dasycarpa . Estimates of base temperature (T b ) and thermal time (θ) for 1/t 50% and leaves d −1 were obtained for each legume cover crop from these functions. Common values of T b were found within each photoperiod response group: 9 °C and 1 °C for 1/t 50% , and 10 °C and −2 °C for leaves d⊃−1&/sup; for short-day and long-day species respectively. Differences among species were represented by variant estimates of θ. The practical consequences of the combined effects of these values of T b and θ for selecting legume cover crops for particular farming systems are discussed.

Photothermal adaptation of sorghum (Sorghum bicolour) in Nigeria

Sorghum is an important crop of the seasonally dry savannas of West Africa adapted to growing periods of 200 days. Locally adapted cvs flower at the end of the rains irrespective of sowing date. Research reported here; (i) reanalysed a sowing date experiment planted at Samaru, Nigeria by Kassam and Andrews in the early seventies to test whether phenology and homeostasis of flowering date in sorghum can be explained by a photothermal model; and (ii) investigated phenological adaptation in Nigeria at four locations between 8 and 13°N by simulating using a photothermal model the duration from sowing to flowering of genotypes originating from latitudes between 6 and 14°N in West Africa using photoperiod and 20 years of daily mean temperature and rainfall data. Phenology was separated into four phases: pre-inductive or juvenile; panicle initiation to flowering; and flowering to maturity, all modulated by temperature; and an inductive phase, modulated by both temperature and photoperiod. The duration of the inductive phase was the major determinant of variation in duration from sowing to maturity. Cultivar SK5912 sown by Kassam and Andrews was acutely sensitive to photoperiod and the thermal duration of the inductive phase was increased by 2115 growing degree days (GDD)/h photoperiod when mean photoperiod is >13 h. The simulations explained how flowering is timed to occur shortly before the end of the rains at the latitudes of cultivar origin, irrespective of sowing date.

Rates of leaf appearance and panicle development in rice (Oryza sativa L.): a comparison at three temperatures

Abstract Plants of rice ( Oryza sativa L., cv. IR36) grown in controlled environment cabinets in free-draining or waterlogged pots at 20, 24 or 28°C with a photoperiod of 11.5 h day −1 were harvested serially and dissected in order to monitor leaf appearance and panicle development on the main culm. Temperature influenced the leaf appearance rate, the leaf number at panicle emergence and the panicle development rates strongly ( P in each case). In contrast, no significant effects of the water-management protocols were detected ( P > 0.25). No abrupt change in the leaf appearance rate was evident at panicle initiation: within each regime, a constant leaf appearance rate quantified relations between the number of emerged leaves and the time from sowing satisfactorily until 10 days after panicle initiation. Between 20 and 28°C linear relations were found between temperature and both the rate of progress towards panicle initiation and the rate of progress towards panicle emergence. In contrast, the rate of leaf appearance was no greater at 28°C than at 24°C; the optimum temperature was about 26°C. Hence, the value of this cardinal temperature differs between foliar and floral development; rice crop growth simulation models need to be modified accordingly.

Flowering of pigeonpea (Cajanus cajan) in Kenya: Responses of early-maturing genotypes to location and date of sowing

Abstract The effects of temperature and daylength on durations from sowing to flowering (f) were studied in six short-duration genotypes of pigeonpea (Cajanus cajan) which had been classified as extra-early or early to mature at ICRISAT Center (17°N). Plants were grown in seven locations in Kenya covering a wide range of altitudes (50–2000 m) at latitudes ranging from 0° to 4°S. Experiments spanned two seasons, and were conducted in normal field conditions as well as under clear polythene enclosures constructed at six of the sites in order to provide warmer than ambient temperatures. All genotypes were also sown at monthly intervals as well as under an artificially extended daylength, both at Katumani (1°30′S). Mean pre-flowering values of temperature (T) and photoperiod (P) varied from 15.6° to 34.0°C and from 12.6 to 15.0 h, respectively. These photothermal conditions resulted in values of f between 53 and 118 d. Rates of progress from sowing to flowering ( 1 f ) were mostly unaffected by but were sometimes slightly responsive to photoperiod, whereas they responded consistently strongly to mean pre-flowering temperature (T) below and above an optimum value close to 24°C. In the sub-optimal range the effects of T were positive and in the supra-optimal range they were negative, such that 1 f =a + bT and 1 f =a′ − b′T , respectively. The genotype-specific parameters a, b, a′ and b′ from these linear-rate models based on flowering responses in 27 environments were validated with independent data. Predicted values in f in 12 monthly sowings (range 62–99 d) did not differ significantly from those observed, i.e. for practical purposes within Kenya, the flowering responses of genotypes classified as extra-early or early to mature are insensitive to photoperiod. At more extreme latitudes (e.g. in India), and given the slight photoperiod sensitivity of some early-maturing genotypes, longer days can combine with supra-optimal temperatures to delay flowering.

Using genotypic variation in flowering responses to temperature and photoperiod to select lentil for the west Asian highlands

A model of the effects of temperature and photoperiod on rate of progress from germination towards flowering has been used to select genotypes of lentil (Lens culinaris Medik.) suitable for winter-sowing in the West Asian highlands. The photothermal model was based on the response of accessions from the world germplasm collection and was used with climatic data from three sites representative of the Turkish highlands in Central and Eastern Anatolia. Use of the model allows more efficient targeting of parent material well adapted to winter-sowing, leading to higher yields than those from traditional spring-sown cultivars. The model suggests that photothermally-insensitive genotypes are poorly adapted to winter-sowing whereas photothermally-sensitive ones are potentially well adapted to these harsh, highland environments. This is compatible with field observations in which only the most photoperiod-sensitive genotype survived winter sowing in two years.

Development in cowpea (Vigna unguiculata). III. Effects of temperature and photoperiod on time to flowering in photoperiod-sensitive genotypes and screening for photothermal responses

Seventeen photoperiod-sensitive genotypes of cowpea ( Vigna unguiculata ) were grown in approximately 30 photothermal environments in Nigeria. Photoperiods ranged from 10 to 16 h d −1 , mean temperatures from 19° to 30°C and times from sowing to flowering ( f ) from 32 to 140 d. Rate of progress towards flowering (1/ f ) was related to mean pre-flowering values of temperature and photoperiod using simple linear rate models comprising one, two or three planes (thermal, photothermal and insensitive). There were no significant differences (p > 0.25) among genotypes in response to temperature within the thermal plane and the common base temperature was estimated to be 7.6°C. Photoperiod-sensitivity varied by a factor of 15 among genotypes, and the critical and ceiling photoperiods varied from 12.2 to 13.4 and from 13.8 to more than 16 h d −1 at a mean temperature of 27°C, respectively. These simple models satisfactorily predicted f in an independent data set (R 2 = 0.62) for plants grown in the main cowpea growing seasons at latitudes between 7° and 13°N. The utility of photothermal models and methods to screen for photothermal responses are discussed.