A jojoba (Simmondsia chinensis [Link] Schneider) stand at Condobolin. N.S.W.. established from a range of plant material, exhibited great variability in a number of plant characteristics including seed yield. Observations over 4 years indicated that a high bud to node ratio is necessary for high yield. Different lines varied from 44 to 74% in this ratio in the fourth year of study. The survival of buds to form open flowers varied greatly between lines and from year to year. Death of flower buds before opening was attributable to frost damage. Buds swelled as early as June in some lines while others showed no sign of swelling until September. In those lines with early swelling or flower opening a high proportion of the buds were frost damaged, whereas late flowering lines had a high rate of survival. Terminal flower buds formed just prior to winter dormancy survived and flowered in the next spring, even in otherwise early flowering lines. Earlier work has shown that jojoba flower buds remain dormant until a chilling requirement has been met. Jojoba lines should have a long chilling requirement to maintain dormancy in the buds until the danger of frosts is past. Almost all of the flowers that opened set fruit, indicating that pollination is not a problem in the New South Wales environment.

Jojoba (Simmondsia chinensis [Link] Schneider) was tested at several sites and on various soil types to assess its production potential under rainfed conditions in semi-arid areas of New South Wales. Stands were established using either plants grown from seed or cuttings taken from selected plants. With good nutrition and weed control, plant height increased at a similar rate over the experiment at all but the most sandy site, where growth was consistently poorer despite similar climatic conditions and management. Stands established from seed had extremely variable yields. Some plants failed to produce seed after 8 years while other plants consistently produced fruit after year 4, with yields as high as 1 kg clean seed per bush by year 8. The average yield was well under 200 g plant-1 except at Trangie in 1986-87 (590 g plant-1). At year 3, 50-100% of female plants were unproductive and by year 8, between 8 and 26% of plants remained unproductive. The variation in yield of the sampled population was consistently high irrespective of seasonal conditions, and usually the upper quartile yield was only marginally higher than the mean. However, the maximum yielding plant produced up to 10 times the mean yield. By contrast, the variation in yield of individuals within a clone was low regardless of the yield potential of that clone and the maximum yielding plant rarely exceeded twice the mean yield. Some clones (A, B and F) show promise as agricultural lines as they are relatively consistent yielders and show early yield development. The highest yield obtained extrapolates to 1.1 t ha-1 at year 7 at a site which averages 417 mm rainfall per year. Further research is needed to identify the reasons for the high variability and fluctuations in yield.

SummaryBranches of jojoba, grown at Condobolin, N.S.W., Australia, were harvested fortnightly from April to September and placed in water in a growth cabinet at 24°C. The percentage of open flowers was recorded three times a week for a period of 28 days and the heat sum (Growth Degree Hours [GDH]) required to open 50% of the flowers was calculated for each harvest date. Each jojoba line was said to have reached the "set-to-open" condition (broken dormancy) when this figure fell below 4800 (18 days in the growth cabinet). The date (or harvest) at which flower bud dormancy broke ranged from April 23 to September 10 for different female lines and from April 23 to August 11 for male lines. Frost damage was apparent by July 25 in plants which broke dormancy early. It was concluded that plants which broke dormancy late had a long chilling requirement and that these plants successfully avoided frost damage to flower buds. These plants would be the most useful lines in a breeding or selection programme for areas which have frost or chill problems.

Jojoba [Simmondsia chinensis (Link) Schneider] cuttings were grown in pots under constant light intensity and vapour pressure deficit at wir temperatures of 18 and 27°C in climate‐controlled cabinets. Leaf conductance and transpiration rate decreased exponentially as the xylen water potential (Ψx) decreased concurrently with the drying out of the soil. At high Ψx’leaf conductance and transpiration rate were much higher at the higher air temperature, and as Ψx declined both parameters decreased more rapidly at 27°C than at 18°C. When soil temperatures were decreased from 27 to 13°C, leaf water potential was not affected at either air temperatures, but transpiration rate was reduced. A linear negative correlation was found between transpiration rates and soil temperatures. It is suggested that the low soil temperature may restrict reducion of water flux in turn reduces stomatal conductance and transpiration without affecting the water potential in the shoot. The releavance of the response to changes in soil or air temperature to the performance of the plant in its semi‐arid habitat is discussed.

Studies in China have shown that fulvic acid (FA), applied after maximum leaf area is achieved, substantially increases the yield of wheat over a wide range of yield levels. The effects were greatest when there was a sustained drought and hot, dry winds. Yield increases appeared to result from the effect that FA had on stomatal conductance and leaf senescence. We report here the responses of predominantly Australian wheat genotypes to FA applied in both glasshouse and field. FA, extracted from coal in Australia or China, was applied to the leaves of wheat plants as a 0.05 or 0.1% spray. Although it reduced stomatal conductance by as much as 55% in particular studies and stimulated the growth of seedlings in other studies, the results were neither consistent nor predictable. We were unable to define a set of conditions under which the maximum effect could always be obtained. In the field studies, three slightly droughted crops were sprayed between late-boot stage and ear emergence. The effects of FA on stomatal conductance were variable amongst treatments 4 h after application, and had virtually disappeared one week later. Grain yield and harvest index were unchanged by FA. Similarly, in glasshouse studies, FA applied to plants at the onset of drought at four stages of development commencing at flag-leaf-emergence had no effect on grain yield or water use. It is concluded that, while FA does appear to have some effects in wheat, we were unable to identify the conditions required for it to influence grain yield and water use. We therefore recommend caution in its use as a foliar spray until these conditions can be defined.

In attempts to determine simple relationships describing the responses of leaf expansion to temperature and radiation, sunflower plants were grown in glasshouses under five temperature and two natural radiation regimes. Crops were also grown in the field at three radiation levels. All leaves, regardless of their position on the plant, fitted a single relationship of relative leaf expansion rate versus leaf age for each regime. These relationships showed that, whilst increased temperature increased the rate of expansion of a leaf at day 1 on our growth scale (approximately unfolding), and reduced the period for which the leaf expanded, each leaf expanded for the same period in day-degree terms regardless of its temperature regime. However this expansion period was modified by radiation such that, for each 1 MJ m-2 day-1 increase, the day-degree sum was reduced by approximately 5°C. The strict inverse relationship between the initial rate of expansion and the expansion period, expressed in days, suggests that at least in some cases the final area of a leaf is largely determined by the stage of 'unfolding'.

Jojoba flower buds break dormancy in response to low temperatures in the presence of adequate water. The possibility that abscisic acid (ABA) is involved in the regulation of dormancy was examined by following endogenous ABA levels in flower buds and leaves and by applying synthetic ()-ABA. Under controlled conditions endogenous levels of ABA were high in dormant flower buds and decreased under conditions of low temperatue that led to flowering. Similar results were obtained in the field. Levels in the leaves were low and changes in response to environmental treatments were small. Daily spraying of the plants with water containing 0.01% Tween enhanced flowering while water stress inhibited it. The application of ()-ABA delayed flowering and reduced the percentage of flowers open at the end of the experiment. An experiment aimed at distinguishing between the effects of temperature and of water status was inconclusive and part of the effect of temperature on ABA may be related to the effect of temperature on the water status of plant.

Seed was collected from jojoba [Simmondsia chinensis (Link) Schneider] plants growing at three field sites in two years. The wax percentage was determined by nuclear magnetic resonance and the compositions of the wax and the ethanolysis products (one site only) were determined by gas chromatography. The mean wax concentration varied from 49.2 to 55.1% over all sites and years. The percentage of long-chain wax esters (>C40) decreased linearly with increase in mean maximum temperature during the period of linear seed growth (r = 0.93). The decrease in long-chain esters was associated with a decrease in the C22 and C24 fatty acids and alcohols. Data from controlled environment studies and from field studies were used to assess the effect of temperature on the percentage elongation, reduction and esterification of acyl-CoAs of carbon lengths 18-22. High temperature lowered the specificity for elongation of C20-C22 and of C22-C,24 and increased the specificity for reduction of the C20 acid to its corresponding alcohol. The amount of C42 wax ester was greater than would be expected by random association of the alkoxy-acyl groups but this preference was not as great at high temperatures.

Jojoba plants were grown in large pots in temperature-controlled phytotron glasshouses. The flowers were hand-pollinated and the seeds were grown under a range of eight temperature regimens from 15/10 to 36/31C (8/16 h; photoperiod 16 h). The concentration of wax in the seed was determined by nuclear magnetic resonance and the wax composition and the composition of the ethanolysis products of the wax were determined by gas chromatography. At 21/16C the wax concentration increased with seed growth until the seed reached 75% of its mature weight and then stabilized at about 45%. The wax concentration in mature seeds was only slightly affected by temperature, except for the extreme treatments of 15/10 and 36/31C where the concentration was reduced. The main effect of temperature on wax composition was the depression of the percentage of waxes with carbon chain lengths greater than 40 at temperatures over 30/25C. This depression was associated with a reduction in the percentage of C22 and C24 fatty acids and alcohols. The effects of temperature will have to be taken into account by plant breeders selecting for high wax content or for a particular wax composition.

Growth of the capsule and seed of jojoba were followed from pollination to maturity at eight temperature regimens ranging from 15/10 to 36/31C (8/16 h; photoperiod 16 h). There was an initial lag before the onset of rapid (linear) seed development, during which the capsule expanded, and this lag varied from 106 days at 15/10C to 7 days at 36/31C. The wax concentration in the seed was low during the initial stages of development, but reached a maximum when the seeds were 70-75% of their final dry weight. The maximum rate of dry matter accumulation in the seed increased with temperature up to 33/28C but, because of the longer growth period at low temperature, seed size at maturity was greatest at 18/13C. The current work suggests that prolonged periods with temperatures above 36/31C, or below 15/10C would be harmful to the development of jojoba seed. The high optimum temperature for growth rate of the seed (33/28C) and sensitivity to a temperature of 15/10C, puts jojoba into the same group as many subtropical species. However, the lower optimum temperature for seed weight at maturity (18/13C) is close to that observed for the temperate cereals.

Well watered mini-crops of sunflower were grown either in summer or winter in glasshouses maintained under five temperature regimes and a 16 h photoperiod. A field crop was grown concurrently with the summer glasshouse study. Summer radiation (25.5 MJ day-1) increased the size and/or number of many of the variables measured compared with winter radiation (9.5 MJ day-1). However, there was interaction between light and temperature upon phenological development, plant height, leaf number and harvest index. Seed production declined at temperatures above 18/13°C in summer and above 24/19°C in winter radiation, but fatty acid composition of the seed oil changed progressively with increasing temperature and was unaffected by radiation. Leaf area per plant increased faster under summer than winter radiation and in almost all temperature regimes reached considerably higher final values which resulted in a greater percentage of the incident radiation being intercepted. Temperature, though affecting the growth patterns and final areas of individual leaves in the canopies, did not alter the relationship between leaf area index and radiation interception. The light extinction coefficient changed with leaf area index and differed between summer and winter. Biomass per plant at maturity (B, g) was best related to radiation interception up to anthesis (I, MJ m-2), such that B = -234 + 541ogl, r2 = 0.91, but seed number (S) was correlated similarly with radiation interception and with the number of degree days (D) accumulated between floral initiation and anthesis (S = 1137+ 0.0051-0.762D, R2 = 0.90). Yield (Y, g per plant) was dependent on seed number, mean temperature (T) and radiation intercepted between anthesis and maturity, and the leaf area present at anthesis. However, over 97% of the variation in yield could be accounted for by the temperature and radiation factors in the manner Y = 39.07+0.047I- 1.26T. Harvest index and yield were not correlated for the cultivar examined.

A method for the routine determination of jojoba wax ester composition and the ethanolysis products of these esters is described. In the recommended procedure, single or half seeds are crushed onto filter paper disks to provide duplicate 10–20 mg samples of the wax. One paper is extracted with petroleum ether for wax ester analysis and the second sample is transesterified in a sealed bottle using 5% HCl in ethanol at 80 C for 1–2 hr. This preparation is extracted with NaCl and petroleum ether, neutralized with potassium bicarbonate and dried with anhydrous sodium sulfate. The fatty acid ethyl esters and free alcohols are determined by gas chromatography (GC). The method requires only small amounts of seed material, provides duplicate samples of the wax, simplifies the ethanolysis procedures and reduces the time needed for the removal of the acid catalyst.

The adaptation of jojoba [Simmondsia chinensis (Link) Schneider] to temperature was studied under controlled conditions. Shoot extension and leaf area development reflected the very low rate of growth of this species, even under favourable conditions, and were stable with an increase in temperature from 20 to 30°C. However growth was markedly reduced at temperatures below 20°C and at 6°C there was no net gain in dry weight over a 42 day period. Root: shoot ratios were near unity and showed a small drop in response to increasing temperature. Leaves adapted to low temperature by an increase in thickness, specific leaf weight and starch content. Chlorophyll formation was retarded in young leaves developing at 15/10°C, but there was no sign of photodestruction of previously formed chlorophyll in mature leaves. Young leaves developing at 30/25°C had a very high chlorophyll a/b ratio of 9.5, but otherwise leaf chlorophyll was apparently normal (2.3-3.4) over a wide range of temperatures. Light saturation of net CO2 exchange (NCE) occurred at about 1000 E m-2 s-1 for leaves grown over a wide range of temperatures and the maximum NCE of approximately 16 mg CO2 dm-2 h-1 (0.45 mg m-2 s-1) occurred between 19 and 25°C. Pulse labelling with 14CO2 indicated that low temperature (18°C) reduced the rate of transfer of 14C from the primary products of fixation to sucrose. The rate of movement of 14C-labelled photosynthate out of the leaf was negligible at 18°C, and reached only about 3% h-1 at 30°C. In the stems, shortly after 14CO2 uptake by the leaf, 86% of the 14C activity was in sucrose, indicating that this was the preferred form of translocate in the vascular system. However glucose was more abundant in the leaves than sucrose, particularly at low temperatures. Starch accumulated in the leaves at low temperatures, reaching nearly 30% of the dry weight at 18/13°C. Photosynthetic stability rather than active adaptation appears to form the basis of resistance to temperature stress in jojoba. With low rates even under optimal conditions this is essentially one of adaptation for survival rather than adaptation for production.

The environmental factors which control the reproductive cycle of jojoba (Simmondsia chinensis [Link] Schneider), were studied under controlled conditions. Plants were placed under a warm pretreatment temperature which resulted in the growth of new shoots bearing dormant flower buds. The plants were later moved to lower treatment temperatures which have been shown to break flower bud dormancy. Pretreatment temperature affected the percentage of nodes which produced flower buds. Both the pretreatment and the treatment temperature affected flowering percentage, there being an optimum pretreatment effect at 30/25C day/night temperatures. Flowering percentage responded to absolute treatment temperature rather than to the drop in temperature from pretreatment to treatment. Flowering percentage increased with decrease in treatment temperature down to 15/10C (male clone) and 12/7C (female clone). The lowest pretreatment-treatment temperature combination was associated with the production of female flower parts on the male inflorescences.

Jojoba (Simmondsia chinensis [Link] Schneid.) is a long-lived desert shrub, valued for the liquid wax which makes up 50% of the seed weight. As attempts are being made to domesticate the species, it is important to understand the environmental factors controlling the reproductive cycle and governing seed yield. The effects of temperature and photoperiod in breaking flower bud dormancy were studied on plants growing under well-watered conditions in controlled environments. Plants 42-48 months old produced only dormant flower buds when growing in 27/22 to 36/31C day/night temperature. When the plants were moved to lower temperatures of 24/19 or 18/13, every plant produced a flowering flush. In two experiments, clonal material was grown at either 30/25 or 36/3lC, then moved to lower temperature treatments. Down to the lowest temperature used (18/13), the greater the drop in temperature, the greater the number of flowers which opened. Flowering occurred under both short (8 h) or long (16 h) photoperiods. There was a critical temperature in the region of 27/22 to 30/25, above which no flowering occurred. Flowering was not dependent on a large diurnal temperature range, but occurred only if the plants were subjected to a low temperature for at least 21 days.

Temperature effects on the growth and yield of wheat (cv. Gamenya) were studied in controlled environments under three day/night temperature regimes (viz. 25/20, 20/15 and 15/10°C) and at three stages of development, viz. vegetative, ear development and grain growth stages. The most important temperature effects were found during the ear development phase. Plants grown at low temperature at this time had long culms, large flag leaves and more potentially fertile florets in each spikelet. The number of florets which produced harvestable grains, and the weight of these grains at maturity, were affected by temperature during the grain growth stage. Temperature prior to floral initiation was not of major importance to final ear weight in this variety, but it did have an effect on the number of mature ears present at harvest. Grain weight per ear at maturity was found to be highly correlated with the number of grains set (r = 0.96), and hence variation in grain number accounted for most of the variation in ear grain weight. In those treatments where grain numbers were not markedly depressed by the temperature treatments, a hlgh positive correlation was found between flag leaf area duration and total grain yield (r = 0.73).