The Effects of Temperature and Daylength on the Rate of Development of Pigeonpea

Eleven cultivars of pigeonpea, representing five different maturitygroups, were grown under controlled conditions to determinehow the rate of development from sowing to flower bud initiation(FBI) and sowing to flowering was affected by temperature anddaylength, the two environmental variables thought to have mostinfluence on reproductive development. Both temperature and daylength had substantial effects overthe range 16–32 C and 10–14 h respectively. Comparisonswithin the 12 h daylength treatment showed no consistent patternwith mean temperature. A discrete-rate analysis was used todetermine the effect on development of each of the temperaturesmaking up the various treatment combinations of day and nighttemperature. The rate of development from sowing to FBI varied among cultivars.The responses to temperature were all strongly curvilinear withoptima between 20 and 24 C. The rate of development from sowingto flowering showed a similar pattern. The effect of daylengthon the rate of development was the greatest between sowing andFBI, with the greatest sensitivity between 12 and 14 h. For the range of conditions considered, temperature had at leastas great an influence as daylength on the rates of developmentfrom sowing to FBI and from sowing to flowering. Some of theresponses to time of planting that have previously been attributedto daylength effects may, in fact, have been due to temperature.The responses to temperature of reproductive and vegetativedevelopment are very different. Phenology, Cajanus cajan     

Estimating the Effects of Varying Temperature on the Rate of Development of Plants

Experiments on the effects of temperature on plant developmentusually yield measurements of the times at which recognizablestages of development are reached, and a record of the varyingtemperature patterns during development. Two complementary methodsfor analyzing such data to reveal the underlying relationshipsbetween rate of development and temperature are discussed. Inboth methods it is assumed that there exists a unique relationshipbetween current rate of plant development and current temperature. In the ‘discrete-rate’ method, the rate of developmentfunction, r(T), is approximated by a set of discrete valuesr₁, r₂...r_i...r_n, each applicable over a given temperature range.The fractional state of development of a plant, S, is writtenas the sum of the products of these rates, r_i, times the fractionof total time during development that temperature was withineach range, f_i, i.e. S = r_i. Systems of such equations can besolved for the r_i, values, and this enables an assessment ofthe rate-temperature relationship without preconceived notionson the form of the plant response. This assessment can then be used as a basis for selecting asuitable interpolation function to be fitted to the data usingthe ‘rate-function’ method. Here a mathematicalform for the function r(T) is selected at the outset. The temperaturescale is divided into discrete intervals and a set of equations,similar to the above, is developed. These equations are solvedfor best values of the parameters of the r(T) function. These methods are illustrated by application to controlled-environmentdata on times from sowing to flowering in soybeans and pigeonpeas,and on rates of leaf appearance in maize. Advantages claimed for the two methods are that they providea systematic approach for relating development to plant temperatureand that they are based upon an explicit physiological hypothesis. Phenology, Zea mays, Cajanus cajan, Glycine max     

The induction of systemic resistance in barley to powdery mildew infection using salicylates and various phenolic acids

Treatment of the first leaves of barley seedlings with either 5, 10, 15 or 20 mM salicylic acid, sodium salicylate or acetylsalicylic acid resulted in significant reductions in powdery mildew infection on the upper, second leaves. In general, the greatest reduction in mildew infection on the second leaves was obtained by spraying the first leaves with a 15 mM concentration of the compounds. Although the largest reduction in mildew infection of the upper leaves was obtained when the compounds were applied to the first leaves 1–2 days before inoculation, very substantial reductions in infection were still obtained if the first leaves were treated 12 days before inoculation. The three compounds had little direct effect on mildew infection. When ¹⁴C-salicylic acid was fed to first leaves of barley seedlings, uptake was rapid and increased with time. Within 6 h, 0.2% of the salicylic acid appeared in the second leaf and by 24 h after feeding, this had increased to 1.4% (1.1 μmol salicylic acid g^-1 fresh wt). The application of various phenolic acids to first leaves also led to reductions in mildew infection on the second leaves. In particular, treatment of the first leaves with 1 mM vanillic acid, isovanillic acid or syringic acid, reduced mildew infection of the second leaves by 81–87%.     

Changes in the Petiole of Leaves of Manihot esculenta (Crantz), on Rooting

The effects of age of leaf and of application of synthetic hormoneon the ability to produce roots, were investigated in leavesof Manihot esculenta. It was found that the age of the leafwas not critical to the process, but that the application ofhormone resulted in an early and prolific production of roots. The anatomy of the rooted petiole was investigated and was foundto differ from that of an unrooted petiole in three respects:in an increase in the amount of secondarily produced tissues;in the incomplete lignification of the secondary xylem and inthe production of adventitious roots from the interfascicularregions of the basal end.     

A second species in the endemic New Caledonian genus Gastrolepis (Stemonuraceae) and its implications for the conservation status of high‐altitude maquis vegetation: coherent application of the IUCN Red List criteria is urgently needed in New Caledonia

A new species in the previously monotypic, endemic New Caledonian genus Gastrolepis (Stemonuraceae) is described. Gastrolepis alticola differs from G. austrocaledonica by its shorter and thicker petioles, strongly coriaceous leaves with revolute margins, shorter inflorescences, and pubescent corollas. The new species is further distinguished by its ecology, occurring only in high‐altitude maquis on two massifs in southern New Caledonia, Mt. Kouakoué and the Montagne des Sources. Gastrolepis alticola is assigned a preliminary conservation status of ‘Endangered’ using the World Conservation Union (IUCN) Red List criteria. Comparison of the IUCN threat status for the 19 species endemic to this distinctive, restricted vegetation type reveals a striking lack of consistency and underscores the need for a reassessment of the entire New Caledonian flora. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 775–783.     

An improved model for simulating the penetration,propagation and absorption of radiation within plant canopies

A mathematical model for simulating the penetration, propagation and absorption of radiation within crop canopies of random leaf distribution is presented. Although the treatment of radiation penetration is based on well known theory, a new approach is developed for tracing the quantity and direction of reflected and transmitted radiation. This approach allows for multiple reflection and transmission up to any required level of accuracy, reflection from the soil, upward as well as downward flux and provides an explicit account of the quantities and direction of scattered radiation. These features will be of most significance at wavelengths where absorption is lowest such as the near-infrared wavebands which are important in remote sensing applications. The approach taken also allows for more flexible consideration of foliage angle which will be most relevant in the photosynthetically active waveband where absorption is high. The predictions of the downward and upward travelling flux densities are compared under ideal conditions with measurements made in canopies of known architecture with three different species, under both clear and overcast skies. Good agreement was obtained in all cases. The expected model deviation in the case of non-random foliage distribution is demonstrated, and the implications for further model development indicated.