Temperature effects on flower formation in saffron (Crocus sativus L.)

The temperature conditions for shoot growth and flower formation were characterised for saffron (Crocus sativus L.). Leaf withering occurred during late winter or spring depending on location, and coincided with a rise in temperature. No growth was detectable in the buds during the first 30 days after leaf withering, neither in underground corms nor in lifted corms incubated in the laboratory under controlled conditions. Flower initiation occurred during the first growth stages of the buds. The optimal temperature for flower formation was in the range from 23 to 27 °C, 23 °C temperature being marginally better. To ensure the formation of a maximum number of flowers, the incubation at these temperatures should exceed 50 days, although incubation longer than 150 days resulted in flower abortion. Flower emergence required the transfer of the corms from the conditions of flower formation to a markedly lower temperature (17 °C). Incubation of the corms after lifting at a higher temperature (30 °C), reduced flower initiation and caused the abortion of some of the initiated flowers. No flowers formed in corms incubated at 9 °C. A variable proportion (20–100%) of the corms forced directly at 17 °C without a previous incubation at 23–27 °C formed a single flower. The wide differences in the timing of the phenological stages in different locations we found in this study seemed related to the ambient temperature. Leaf withering was followed shortly by flower initiation, which occurred during late spring or early summer as the rising temperature reached 20 °C. A long hot summer delayed flower emergence which occurred in late autumn as the temperature fell to the range of 15–17 °C.     

Reduction of chilling injury in ‘Tommy Atkins’ mangoes during ripening

Studies were conducted to investigate how harvest maturity influence fruit ripening processes to alleviate chilling injury (CI) in mangoes (cv. Tommy Atkins). Fruit at three stages of maturity, immature (M1), half-mature (M2) and mature (M3) were stored for 18 days at 5 °C and then at 1 or 3 days at 20 °C. M1 fruit succumbed to CI after 18 days at 5 °C, with symptoms increasing in severity upon warming. Low C₂H₄ production, poor colour development, minor changes to fruit composition, insipid flavour and poor aroma revealed that fruit ripening was insufficient to reduce CI compared to M2 and M3 fruits. M2 and M3 fruits had higher C₂H₄ production rates than M1 fruit and ripened normally with acceptable flavour and aroma after 18 days at 5 °C and 3 days at 20 °C. While M3 fruit had no CI symptoms, they were overripe and fruit decay incidence was 26.6%, compared to M2 fruit which had no decay, a trace of CI symptoms and possessed the best overall quality.     

Temperature and irradiance effects on Sandersonia aurantiaca flower shape and pedicel length

Sandersonia flowers can vary from being lantern- to tubular-shaped. Lantern-shaped flowers are considered to be most commercially desirable when the ratio of the widest to the narrowest diameters of a flower, termed the ratio of hips to waist, is 1.5 or greater. Pedicel length can also affect the overall appearance of a flower stem. Short pedicels are considered more desirable. The influences of temperature and irradiance on Sandersonia aurantiaca flower shape and pedicel length were examined in controlled environment (CE) growth rooms. The growing environments were at constant temperatures of 15, 18, 21, 24 or 27 °C; or day/night temperature differentials of −6, 0, +6, +12, or +18 °C, with a mean of 21 °C. Photosynthetic photon flux densities (PPFD) were 700, 460 or 210 μmol m⁻² s⁻¹. At harvest, measurements were made of the widest and narrowest diameters of the oldest flower on each stem and the ratio of these parts was calculated. The pedicel length of the oldest flower was also measured. Environments with constant temperatures below 23 °C and the least day/night temperature differentials (−6, 0 and +6 °C) produced flowers of the most desirable shape, defined as having a hips to waist ratio of 1.5 or greater. At these temperatures, irradiance had a variable effect on flower shape. Pedicel length was also highly dependent on temperature and PPFD. As mean temperatures increased or as the temperature differential changed towards a differential of 12 °C, and as PPFD decreased, pedicel length increased significantly. Hip diameter was more sensitive to environmental changes than waist diameter and thus had a greater effect on flower shape. This work indicates to growers that they can enhance Sandersonia flower quality by producing more desirably shaped flowers with short pedicels through maintaining relatively low (less than 23 °C) mean temperatures, minimising temperature differentials, and maintaining irradiance levels as high as possible.     

Production of high quality Ardisia plants by stem tip cuttings

To produce commercially acceptable Ardisia plants, stem tip cuttings from mature plants were rooted and forced in greenhouses. Ten centimeter long cuttings were either treated with 200 ppm 1-naphthalene acetic acid (NAA) for 2 h, 2000 ppm indole-3-yl-butyric acid (IBA) for 10 s, or 0.5 and 1.0% IBA powder prior to sticking them in the rooting medium. Rooting percentage at 45 days exceeded 76% with 2000 ppm IBA treatment which was a significant increase over non-treated control. Rooted cuttings developed into three types of plants: those forming only vegetative shoots without flowers, those forming reproductive shoots with flowers, and those forming both vegetative and reproductive shoots. The ideal plant produced only vegetative shoots when rooted cuttings were transplanted into pots. About 50% rooted cuttings were forced to finish, producing 31 or 40% of high quality plants when rooted cuttings with vegetative shoots were grown in a greenhouse (GH) at temperatures higher than 21/19 °C (day/night) in 1995 or 21/18 °C GH in 1997, respectively. This method shortened the total production time to less than 2 years as compared to 4 years when starting from seeds.     

The temperature and photoperiod regulation of flowering and runnering in the strawberries,Fragaria chiloensis,F. virginiana,and F. x ananassa

The temperature and photoperiod interactions of a number of elite genotypes of Fragaria virginiana, F. x ananassa, and F. chiloensis were studied in a series of growth chamber experiments. Several parameters were evaluated including: (1) the critical day-length (CDL) for flowering of short day (SD) genotypes under 8, 9, 10, and 11 h days at 18 °C, (2) the floral and runnering response of single and multiple cropping genotypes under 8 and 16 h days at 18 °C, and (3) the effect of temperature on flower bud formation in day-neutral (DN) genotypes held at 18, 22, 26, and 30 °C under 12 h day-lengths. The same number of flowers were initiated under 15 and 30 day induction periods, regardless of photoperiod. Frederick 9, LH 50-4 and RH 30 (F. virginiana), ‘Aromas’ and ‘Tribute’ (F. x ananassa) and CFRA 0368 of F. chiloensis flowered under both long days (LDs) and SDs; while Eagle-14 (F. virginiana), ‘Fort Laramie’ and ‘Quinalt’ (F. x ananassa) flowered only under long days. While those genotypes that flowered under both LD and SD can be considered day-neutral, they varied in the degree of floral response to the two photoperiods. CFRA 0368 and Frederick 9 produced the same number of flowers under both LDs and SDs, while ‘Aromas’ and ‘Tribute’ had more flowers under LDs and RH 30 had more under SDs. Of the DN genotypes, LH 50-4 and RH 30 were the only ones that produced runners under SDs. Flowering in ‘Fort Laramie’ was least affected of any genotype by high temperature, although its dry weight was negatively impacted. Based on these data, several genotypes show promise as breeding parents: CFRA 0368 and Frederick 9 to equalize flower production under LD and SD conditions, LH 50-4 and RH 30 to produce more freely runnering DNs, and ‘Fort Laramie’ for floral heat tolerance.     

Temperature effects on corm dormancy and growth of Zephyra elegans D.Don

Experiments were performed with the Chilean geophyte Zephyra elegans, a potential cut flower, to evaluate the effect of corm weight and storage temperature on corm dormancy, and to determine the effect of day and night growing temperatures on its growth and flowering. Z. elegans has a deciduous and synanthous growth habit and the corm is replaced annually. Dormant corms were stored at different constant temperatures or temperature combinations from 20 to 40 °C. Corms released from their dormancy were grown at 15/10, 20/15, or 25/20 °C day/night temperatures. Corms of various weights were planted at the same date after being stored dry at 25 °C for 22 weeks. They all emerged 19–38 days after planting, showing that dormancy release was not affected by corm weight. A 20-week corm storage treatment at a constant 25 °C resulted in the most rapid corm sprouting. Sprouting percentage was reduced at higher or lower storage temperatures. Temperature also affected plant growth. When plants were grown at 15/10 or 20/15 °C they emerged and flowered more rapidly than when they were grown at 25/20 °C. The latter growing temperature also resulted in poor flower quality.     

Day and night temperatures,daily light integral,and CO2 enrichment affect growth and flower development of Campanula carpatica ‘Blue Clips’

Campanula carpatica Jacq. ‘Blue Clips’ plants were grown in a greenhouse under nine combinations of day and night temperatures created by moving plants every 12 h among three day/night temperatures (15, 20, and 25°C). At each temperature, there were three daily light integrals (DLI; 4.2, 10.8, and 15.8 mol m⁻² per day, averaged over the experimental period) created with varying supplemental light, and ambient (≈400 μmol mol⁻¹) and enriched (≈600 μmol mol⁻¹) CO₂ concentrations. Time to flower was closely related to average daily temperature (ADT), and was not significantly affected by the day or night temperatures delivered to achieve a specific ADT. Time to flower was not largely affected by DLI or CO₂ enrichment. As plant ADT increased between 15 and 25°C, flower diameter decreased about 1 mm per degree and was not related to the difference between day and night temperatures (DIF). Flower diameter was smallest and least sensitive to changes in temperature at lower DLI and at ambient CO₂ levels. There were 10 less flower buds and 0.3 g less dry mass per plant at first flower for every 1° increase in plant ADT at high and medium DLIs. Flower bud number and dry mass were relatively low and less sensitive to changes in ADT at low DLI, and increased slightly with CO₂ enrichment at medium and high but not at low DLI. Plant height was not related to ADT, but increased linearly as DIF increased from −6 to 12°C at all DLIs, but the response was stronger under low DLI than high and medium DLIs. Flower bud number and dry mass were correlated closely with the ratio of DLI to daily thermal time (base temperature of 0°C). Flower bud number and dry mass were highest when C. carpatica plants were grown at 15°C with a DLI of 10–15 mol m⁻² per day.     

Bruising injury of persimmon (Diospyros kaki cv. Fuyu) fruits

This study was performed to monitor the deterioration of bruised persimmon (Diospyros kaki cv. Fuyu) fruits. Freshly harvested fruits were bruised by dropping them from a height of 50 cm onto a steel board and then stored at 0 or 20 °C in temperature controlled chambers for up to 4 weeks. Immediately after the bruising, no visible injury on the fruits was evident, but the fruits deteriorated rapidly during storage. The skin tissues of the fruits stored at 20 °C became more reddish with the duration of the storage, but no such changes were found with the fruits stored at 0 °C. The increase in redness of the skin tissues appeared to be associated with storage temperature, but not with the bruising. The skin tissues also became darker when stored at 20 °C than at 0 °C and this tendency was more obvious with the bruised fruits. Flesh firmness decreased rapidly during storage except for the non-bruised fruits stored at 0 °C. Even the non-bruised fruits rapidly lost their flesh firmness at 20 °C. No significant changes in lipid peroxidation, as expressed by malondialdehyde production, were found between the bruised and the non-bruised fruits during the storage either at 0 °C or at 20 °C. This implies that the fruit deterioration caused by bruising is not due to the consequences of lipid peroxidation. Polyphenol oxidase activity increased more rapidly in the bruised fruits than in the non-bruised fruits during storage. The bruising had more effect on increasing polyphenol oxidase activity than did the storage temperature. Although the increase in polyphenol oxidase activity appeared to be associated with the visual deterioration of the bruised fruits, it did not exactly correspond to the physical deterioration. These results indicate that polyphenol oxidase is not the only factor influencing the deterioration associated with bruising. Cell wall hydrolases are currently being assayed to determine if they also contribute the deterioration following bruising.     

Freezing temperature treatment induces bud dormancy in ‘Granny Smith’ apple shoots

One-year-old, ‘Granny Smith’ apple (Malus × domestica Borkh.) shoots were selected randomly from commercial orchards in 1999 and 2003, cold stored at temperatures between 1 and 13 °C for varied periods, following a 12/12 h freezing temperature pre-treatment of −1/13 °C (supposedly non-chilling temperatures) for 1 or 2 weeks. The rate of budburst, determined after forcing at 25 °C, was used to follow the progression of bud dormancy. The freezing pre-treatment clearly enhanced (deepened) bud dormancy in all experiments. Clearly definable influences due to the presence of leaves during the pre-treatment were not observed on shoots cold stored at chilling temperatures. Trees were defoliated before leaf drop in late summer/autumn under field conditions by hand (2001) and using a spray containing 3% urea and 1.8% zinc sulphate in 2003. In 2001 the first two hand defoliation dates significantly enhanced dormancy, while in 2003 chemical defoliation had no effect. These data indicate that the leaves are not clearly involved in the perception of factors that are responsible for dormancy induction. As with dormancy release it is possible that the perception of induction factors, i.e. low temperatures, and as shown in these data, freezing temperatures, occurs within the buds themselves.     

Embryo induction via anther culture in papaya and sex analysis of the derived plantlets

We investigated the embryo induction of papaya by anther culture, and identified the sex of plantlets derived from embryos using a sex-diagnostic PCR. Anthers, containing approximately 80% uninucleate pollen, were collected from 10 to 14 mm long male flower buds. They were pre-treated on agar (0.8%) or in liquid medium for 1–5 days at 25 or 35 °C, then transferred to agar medium with 0.1 mg l⁻¹ BA and 0.1 mg l⁻¹ NAA. Agar and liquid media used for the pre-treatment contained water only or MS nutrients with or without sucrose (2.0%). On the agar medium, no embryos were induced at any pre-treatment temperature. In the liquid medium at 25 °C, embryos were induced at about 1.0% (rate of anthers forming embryos) in MS medium with sucrose for 3 or 5 days. At 35 °C, embryo induction rate tended to increase up to about 4.0% when anthers were treated in water for 1 day or MS medium with sucrose for 3 or 5 days. The sex of plantlets established through anther culture was analyzed using a sex-diagnostic PCR. All plantlets were determined as female. From these results, we suggest that all plantlets established through anther culture were of microspore origin, and that the anther culture technique is useful for the breeding of female papaya.     

Analysis of rhythmic growth in holly (Ilex × meserveae) grown in controlled conditions

The influence of 24 h mean air temperature (18.3, 20.6, 23.9 and 25.8 °C) and photosynthetic photon flux (PPF; 0.6, 2.1, 3.7 and 4.7 mol m⁻² d⁻¹) on the growth cycles of vegetative growth in Ilex × meserveae (‘Blue Princess’ S.Y. Hu) was investigated. Plants propagated from top cuttings were grown in greenhouse compartments. The number of unfolded leaves was recorded continuously throughout the experiment. A modified sine function was fitted to collected data and the values for the amplitude and frequency of the growth curves were analysed. The sine function was tested as a method to evaluate the influence of climate on periodically flushing species. Both amplitude and frequency were significantly influenced by air temperature and PPF. The highest frequency of flushing was found at 23.9 °C and 3.7 mol m⁻² d⁻¹. The function resulted generally in a good fit to collected data with R² values above 0.9. Growth curves of all individual plants were categorised with respect to their growth pattern as poor synchronisation within the treatments did not allow analysis of the mean values of the growth curves.     

Improvement of in vitro micropropagation of Lilium oriental hybrid ‘Casablanca’ by the formation of shoots with abnormally swollen basal plates

Bulb scales of Lilium oriental hybrid ‘Casablanca’ were cultured on MS medium supplemented with cytokinins (kinetin, BA (benzyladenine), TDZ (thidiazuron)). The basal part of bulb scales swelled and formed adventitious shoots with foliage small, leafy bulb scales and abnormally swollen basal plates on the media with cytokinins. Shoots were formed rapidly from the basal parts of bulb scales and became shoot clusters. The medium containing 2.2 μM BA was most favorable in the shoot formation from bulb scales. Cutting shoots into small segments (7–8 mm wide × 12–15 mm length) were cultured on media containing BA and IAA (indole acetic acid) and the segments regenerated many new shoots and formed shoot clusters. The shoot section to shoot cluster cycle method improved adventitious shoot proliferation. The media supplemented with 4.4 μM BA and 5.7 μM IAA. or 8.9 μM BA and 0.6–2.9 μM IAA were effective in allowing the proliferation of shoots from shoot segments under light condition. Sucrose and activated charcoal (AC) improved bulblet growth. Bulblet growth was effectively performed on MS medium containing 60 g/L sucrose. Bulblet growth was also improved by the supplement of AC. The medium with 2.0 g/L AC was most effective for bulblet growth. Normal bulblet growth was stimulated more by the culture of shoots than that of bulb scales. Bulblet weight from shoots reached to an average of over 1100 mg of a bulblet after 3 months in culture on MS medium containing 60 g/L sucrose and 2 g/L AC. Most of the bulblets produced by this method generated stems with several leaves in the green house, after cold treatment at 5 °C for 3 months.     

Environmental factors affecting flowering of rice flower (Ozothamnus diosmifolius,Vent.)

Rice flower (Ozothamnus diosmifolius, Vent.), native to east Australia, is a spring flowering perennial shrub. It is a new cut flower plant, recently introduced into cultivation in Australia and in Israel. Its response to environmental conditions, which affect growth and flowering, are not yet known. The purpose of the present study was to evaluate the effects of growth temperature, photoperiod and total solar energy on flowering. Experiments were conducted with plants of the cv. Cook’s Snow White. Plants were grown in three cycles under controlled conditions in the phytotron, at four day/night temperature regimes: 17/9, 20/12, 23/15 and 26/18°C. Two photoperiods — short day (SD) of 10 h natural day light and long day (LD) of 10 h natural light plus 10 h incandescent light — were employed. High temperatures enhanced vegetative growth but blocked flowering under both LD and SD. Under medium–moderate temperatures plants were absolute LD plants and did not flower under SD conditions. Under lower temperatures plants flowered under both LD and SD, but SD delayed flowering. High total solar radiation under LD did not affect flowering time but greatly promoted the number of flowering stems.     

Effects of pre-blossom temperatures on flower development and fruit set in apricot

The influence of pre-blossom temperatures on flower development and fruit set is ascertained in apricot (Prunus armeniaca L.), a species without previous records on the effect of pre-blossom temperature on fruit set, but that is particularly prone to erratic fruit set. A polyethylene cage was used during pre-blossom development of flower buds to increase maximum temperatures by 6–7 °C and mean temperatures by 3 °C in orchard conditions. This increase in temperature accelerated flower bud development, caused a hastening in flowering time and following hand-pollination, reduced fruit set. At anthesis, flowers that had developed in warmer conditions weighed less and showed less development of the pistil than control flowers. Pistil growth of flowers under warm conditions did not differ from that of the control flowers when both the populations were compared on a real time scale in spite of the fact that warmed buds were at an advanced external phenological stage. Thus, hastening of external floral development by warm pre-blossom temperatures was not accompanied by advance in pistil development. This lack of synchrony resulted in premature flowering of flowers with underdeveloped pistils that had a reduced capability to set fruit. The results are discussed in terms of flower quality and its implications in fruit set and subsequent crop load.     

Effect of photoperiod on flower bud initiation and development in myoga (Zingiber mioga Roscoe)

Selection of suitable production locations in Australia and New Zealand for production of myoga (Zingiber mioga Roscoe) has been limited by lack of information on climatic influences on flowering. This study focused on photoperiod as potential production sites within Australia differ considerably in daylength due to the geographical range. The two cultivars available in Australia (Inferior and Superior) were examined in this trial due to previously observed differences in vegetative and reproductive development.Plants grown under long-day conditions (16 h) and short-day conditions (8 h) with a night break produced flower buds, while those under short-day conditions (8 h) did not. The failure of plants under short-day conditions to produce flower buds was due to abortion of developing floral primordia rather than a failure to initiate inflorescences. It was concluded that for flower development in myoga a qualitative long-day requirement must be satisfied, but that flower initiation was day-neutral.Short-day conditions resulted in abortion of flower primordia, premature senescence of foliage and reduced foliage dry weight in both cultivars. Early senescence and low flower bud yield of the Inferior cultivar, but not the Superior cultivar have been observed in crop evaluation trials in Southern Australia and New Zealand. Differences in critical photoperiod between the two cultivars may explain this observation and therefore photoperiodic requirements may be an important consideration in site and planting date selection for different cultivars.     

Flowering of Primula malacoides in response to photoperiod and temperature

Primula malacoides Franch. ‘Prima Lilac’ was grown at 16 or 20 °C in combination with short days (SD, 8 h) or long days (LD, 16 h). In addition to uninterrupted growing conditions, plants within each temperature were moved at weekly intervals to the other photoperiod and left until termination. Temperature, but not photoperiod, significantly affected the rate of development from start of treatments (51 days from seeding) to 2 mm visible flower bud (VB). At 16 °C, VB averaged 30 days and at 20 °C, 48 days. Time to flower (first horizontal petals) at 16 °C increased from 56 to 64 days as SD increased from 1 week to continuous conditions while LD decreased time to flower from 64 to 56 days. Time to flower at 20 °C varied from 73 to 87 days with additional SD exposure resulting in slower and LD in faster flowering. These observations of the flowering response in ‘Prima’ are contrary to the photoperiodic classification of P. malacoides as a SD plant.     

Effect of maleic hydrazide on endogenous cytokinin contents in lateral buds,and its possible role in flower bud formation on the Japanese pear shoot

In order to elucidate the role of maleic hydrazide (MH, 1,2-dihydro-3,6-pyridazinedione; coline salt) in increasing flower bud formation on the Japanese pear, the effect of MH on cytokinin contents in the lateral buds of Japanese pear shoots were investigated. Foliar application of MH at 2600 mg l⁻¹ increased zeatin, zeatinriboside, and isopentenyladenine levels in lateral buds though isopentenyladenosine concentration decreased. Application of 2,3,5-triiodobenzoic acid (TIBA), an inhibitor of polar auxin transport, also increased the endogenous cytokinin levels in lateral buds. It is supposed that these increases of cytokinin in lateral buds may be involved in the increase of flower bud production on the Japanese pear shoot. The increases of cytokinin induced by these chemicals may be caused via the depletion of the auxin level and/or the activity in shoot tissues.     

Direct shoot organogenesis on shoot apex from seedling explants of Capsicum annuum L.

In vitro direct multiple shoot formation from seedling explants of Indian high pungent varieties of Capsicum annuum cv. Arka Abhir (AA) and Arka Lohit (AL) was successfully obtained. We were able to induce regeneration potency in these varieties by inverting the explant. Aseptically grown seedling explants with decapitated roots, apical meristem and cotyledonary leaves were inoculated in an inverted position in bud induction medium comprising of Murashige and Skoog's basal medium supplemented with 2-(N-morpholine) ethanesulphonic acid (MES) buffer along with 26.63 μM benzyl adenine (BA), 2.28 μM indole-3-acetic acid (IAA) and 10 μM silver nitrate. Profuse shoot bud induction with 20–25 shoot buds per explant was obtained. Supplementation of phloroglucinol in the bud induction medium resulted in 17 and 18% enhancement in bud induction response in Arka Abhir and Arka Lohit variety, respectively on the inverted hypocotyls. Auxin transport inhibitor tri-iodo benzoic acid (TIBA) in the bud induction medium resulted in induction of buds in a shorter period of 40–45 days when compared to bud induction (BI) medium which takes 55–65 days for bud induction. These buds were transferred to MS medium containing 2.8 μM gibberellic acid and 10 μM silver nitrate resulting in elongation of shoot buds. Transfer of shoots to MS basal medium induced rooting to produce plantlets. This protocol can be efficiently used for mass propagation and presumably also for regeneration of genetically transformed C. annuum tissues.     

Inhibition of flowering of Mexican- and Guatemalan-type avocados under tropical conditions

Avocado trees of a range of cultivars growing in Darwin, northern Australia (average yearly maximum 33°C, minimum 23°C), were observed for flower and shoot development. Terminal buds of the cultivars ‘Fuerte’, ‘Rincon’ and ‘Edranol’ sampled in July were not floral. Buds which did not burst were sampled in September and they contained developing flowers with perianth primordia. Vegetative extension growth resulted from laterals proximal to the inhibited terminal buds.Avocado trees of the cultivars ‘Fuerte’ and ‘Hass’ which had initiated floral buds were transferred to controlled environment chambers with 33°C day, 23°C night ($\text{33}\text{23}$) or 25°C day, 15°C night ($\text{25}\text{15}$) with a 12-h photoperiod and photon flux density of 400 μmol m^?2 s^?1 (400–700 nm). At $\text{33}\text{23}$ the trees had fewer flowers and a shorter flowering period than at $\text{25}\text{15}$. Inhibited floral buds and lateral vegetative extension resulted at $\text{33}\text{23}$, as observed in northern Australia. The unburst buds had developing flowers with perianth and stamen primordia.The controlled environment experiments showed that the abnormal flushing behaviour of Mexican- and Guatemalan-type avocados growing in northern Australia was due to high temperature. Floral development was inhibited at the stage of stamen differentiation.     

Influence of temperature and bark injuries on the development of Phytophthora cactorum and P. Citrophthora on peach trees

The effect of temperature and bark injuries on the occurrence of crown rot of peach trees caused by P. cactorum and P. citrophthora were examined in field and laboratory. Lesions developed at 35 °C (the complete range of temperatures tested) but maximum development occurred at 20–25 °C. Greatest growth of these fungi on cornmeal agar (CMA) also occurred between 15 and 30 °C. Both pathogens could infect injured trees up to 20 days after wounding, but could not infect uninjured plants or plants wounded 40 and 30 days before inoculation, respectively. This study showed that temperature is a critical factor for the development of Phytophthora crown rot of peach trees. In addition, crown rot developed from recent wounds inoculated with agar plugs of Phytophthora.