Aerosol Survival of Pasteurella tularensis Disseminated from the Wet and Dry States

The aerosol survival in air and in nitrogen was measured for Pasteurella tularensis live vaccine strain, disseminated from the wet and dry states. The results showed that most of the loss of viability occurred in less than 2 min of aerosol age, i.e., a rapid initial decay followed by a much slower secondary decay. In nitrogen and air, minimum survival occurred at 50 to 55% relative humidity (RH) for wet dissemination and at 75% RH for dry dissemination. This shift indicated that aerosols produced by wet and dry dissemination were not equivalent and suggested that survival might not be related to bacterial water activity or content. The results showed that rehydration is the key process with regard to survival, but that lysis on rehydration is not a primary death mechanism. The effects of oxygen were complex because it could be either protective or toxic, depending upon other conditions. The protective action of oxygen was through an effect on the spent culture suspending fluid. The latter contained a toxic component, the activity of which is suppressed by oxygen; possibly the component is pumped away during freeze-drying. A toxic effect of oxygen was not found in the presence of spent culture media because the toxicity of the latter masks such an effect. With other bacterial suspending fluids, oxygen was shown to be toxic at low RH. Similar effects with regard to oxygen toxicity were also found with a laboratory strain of P. tularensis. Differences in oxygen toxicity for aerosols generated from the wet and dry states also suggest that bacterial water content and activity do not control aerosol survival.     

Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Pollen of the palm Trachycarpus fortunei was kept at 25°C and relative humidities (RH) of 20, 55 and 98%. Changes in viability, water content and carbohydrates were measured over 2–17 days. Water content remained almost constant at 20 and 50% RH and increased dramatically at 98%. Pollen viability and germination rate remained almost constant over 14 days at 20% RH and decreased to about 2% after 7–9 days at 55% and to even less at 98% RH. Although the three experimental conditions were constant, qualitative and quantitative variations in pollen carbohydrates were recorded, even after pollen had lost its viability. The quantities of mono-, di- and polysaccharides varied with the period of pollen storage at the various RH. The greatest changes in glucose, fructose and sucrose content were recorded at 55 and 98% RH. At these relative humidities, maximum glucose and fructose content and minimum sucrose content occurred at maximum water content. Starch was not present in mature pollen but appeared and peaked after 7–9 days of pollen storage at 55 and 98%. Appearance of starch coincided with an increase in pectin content. PAS-positive cytoplasmic polysaccharides showed an increasing trend at 20% RH. A relation was found between pollen viability, water content and monosaccharide content. Pollen viability and germination capacity remained high at 20% RH for 14 days. At this relative humidity, pollen water, glucose and fructose contents remained almost constant, while sucrose reached its maximum value. The fluctuations of more complex carbohydrates (starch, pectins and PAS-positive cytoplasmic polysaccharides) were less easy to interpret. Changes observed under experimental conditions could simulate processes occurring in nature during pollen presentation and dispersal.     

Biological assessment of Tetrastichus brontispae,a pupal parasitoid of coconut leaf beetle Brontispa longissima

To control coconut leaf beetle, Brontispa longissima (Gestro), the pupal parasitoid Tetrastichus brontispae Ferrière was imported from Taiwan and its biology was studied in quarantine in Hainan, China. The parasitoid development includes an egg, three larval instars and three pupal stages. Its developmental time from egg to adult was 19.5±0.5 days under conditions of 24±2°C and 75±5% relative humidity (RH). Temperature had no effect on the sex ratio of offspring, but significantly affected the parasitism rate and reproduction. The parasitism rates were 98.07, 97.97 and 95.03% at 28, 24 and 20°C, respectively, whereas the parasitism rate was 52.18% at 18°C and 69.48% at 30°C, respectively. Furthermore, the parasitoids reared at 18 and 30°C produced fewer offspring than those at 20, 24 and 28°C, respectively. With the increase in temperature, developmental time decreased linearly from 46.19 days at 18°C to 17.10 days at 28°C. RH significantly influenced development, parasitism rate and the reproduction of T. brontispa. With the decrease of RH, developmental time increased from 22.94 days at 20% RH to 18.84 days at 95% RH. In contrast, parasitism rate and the number of offspring per female increased with the increase of RH. Though emergence rates between 50 and 95% RH were much higher than those between 20 and 35% RH, the sex ratios between 20 and 95% RH were not different. Photoperiod had no effect on parasitism, the number of offspring per female, emergence and the sex ratio of T. brontispae, but developmental time was significantly different for different photoperiods. Sucrose, honey and glucose significantly enhanced adult longevity, parasitism and the number of offspring per female of T. brontispae, but had no effect on the sex ratio and survival. Females of T. brontispae only parasitized fourth to fifth larval instars and 1–5-day-old pupae, but there was a significant difference in the number of offspring per female, development time, emergence and the sex ratio of offspring in different instars. These results showed that 1-day-old pupae, a temperature of 24–28°C and 65–95% RH were optimal for T. brontispae. These findings should be helpful in developing a production system to rear and release T. brontispae in large enough quantities to effectively control coconut leaf beetle.     

Use of Coating to Protect Lyophilized Bacillus popilliae from Moisture

Lyophilized cells of Bacillus popilliae were protected from moisture when suspended in pellets of tung oil polymer which were then coated with paraffin wax. The survival of the protected cells at various levels of relative humidity (RH) and under various storage conditions was determined. During 6 months of storage, moisture appeared to have little effect on survival of the cells when the RH level was 22% or less; but, at higher RH levels, survival declined upon storage. Viable cells were recovered when pellets were stored for 3 months at 33% RH, 2 months at 42% RH, 1 month at 50% RH, and 4 days in distilled water. Under field conditions, some cells survived at least 1 week of storage.     

Influence of Different Storage Conditions on the Mycotoxin Production and Quality of Fusarium-Infected Wheat Grain

Wheat seed samples with different initial infection levels of Fusarium culmorum were kept under different storage conditions for 36 weeks. Samples for analysis were drawn before storage and at intervals of 6‐8 weeks to determine the mycotoxin contents, seed health and seed quality. Zearalcnone (ZEA) accumulated to higher kernel contents towards the end of storage, when the seed was stored under warm and humid conditions [25°C/90% relative humidity (RH)], whereas the deoxynivalenol (DON) content of severely infected kernel samples (> 50%) remained unchanged under any of the conditions. On the other hand, DON contents increased in samples with a slight (4%) or moderate (15%) Fusarium infection level. when the seed was stored under Warm and humid conditions. Nivalenol (NIV) was not found in any samples immediately after harvest but later on in storage, and only under cool or warm but very humid conditions (15°C/84% RH and 25°C/90% RH). During storage, the mycotoxin contents of the samples did not reflect the percentage of Fusarium infected kernels. Under warm but dry conditions (25°C/62% RH) the seed germination rate showed a slight increase or remained nearly constant; at the same time the Fusarium infection level of the kernels decreased fairly fast. Cool and dry conditions (15°C/56% RH) maintained good seed quality but the Fusarium infection level of the kernels remained largely the same. Warm and humid conditions are not appropriate to maintaining quality of both seed and grain product.     

Studies on the prolonged storage of Metarhizium anisopliae conidia: effect of growth substrate on conidial survival and virulence against mosquitoes

Metarhizium anisopliae was grown on six complex mycological media and on three types of rice at three moisture levels to determine the effect of growth substrate on conidial yield, viability, and virulence against mosquitoes immediately after spore maturation and after the storage of conidia at four different temperature-relative humidity (RH) combinations over a 1-year period. Conidial yields varied with the mycological media, but the viability and virulence of conidia against mosquitoes produced on all substrates were similar when spores were stored under the same conditions. The storage conditions were more critical to spore survival and virulence than the substrate upon which conidia were produced. The comparison of rice types for conidial production indicated that conidial yield, viability, and virulence to mosquitoes were more dependent upon the moisture level during growth and on the storage conditions that upon the rice used. The best storage conditions among those tested for the retention of both spore viability and virulence against mosquitoes were 19°C–97% RH and 4°C–0% RH.     

Desiccation tolerance and drought acclimation in the Antarctic collembolan Cryptopygus antarcticus

The availability of water is recognized as the most important determinant of the distribution and activity of terrestrial organisms within the maritime Antarctic. Within this environment, arthropods may be challenged by drought stress during both the austral summer, due to increased temperature, wind, insolation, and extended periods of reduced precipitation, and the winter, as a result of vapor pressure gradients between the surrounding icy environment and the body fluids. The purpose of the present study was to assess the desiccation tolerance of the Antarctic springtail, Cryptopygus antarcticus, under ecologically-relevant conditions characteristic of both summer and winter along the Antarctic Peninsula. In addition, this study examined the physiological changes and effects of mild drought acclimation on the subsequent desiccation tolerance of C. antarcticus. The collembolans possessed little resistance to water loss under dry air, as the rate of water loss was >20% h(-1) at 0% relative humidity (RH) and 4 degrees C. Even under ecologically-relevant desiccating conditions, the springtails lost water at all relative humidities below saturation (100% RH). However, slow dehydration at high RH dramatically increased the desiccation tolerance of C. antarcticus, as the springtails tolerated a greater loss of body water. Relative to animals maintained at 100% RH, a mild drought acclimation at 98.2% RH significantly increased subsequent desiccation tolerance. Drought acclimation was accompanied by the synthesis and accumulation of several sugars and polyols that could function to stabilize membranes and proteins during dehydration. Drought acclimation may permit C. antarcticus to maintain activity and thereby allow sufficient time to utilize behavioral strategies to reduce water loss during periods of reduced moisture availability. The springtails were also susceptible to desiccation at subzero temperatures in equilibrium with the vapor pressure of ice; they lost approximately 40% of their total body water over 28 d when cooled to -3.0 degrees C. The concentration of solutes in the remaining body fluids as a result of dehydration, together with the synthesis of several osmolytes, dramatically increased the body fluid osmotic pressure. This increase corresponded to a depression of the melting point to approximately -2.2 degrees C, and may therefore allow C. antarcticus to survive much of the Antarctic winter in a cryoprotectively dehydrated state.     

Optimal hatching conditions of Zophobas atratus (Coleoptera: Tenebrionidae) eggs under various culture conditions

Supermealworm, Zophobas atratus (Coleoptera: Tenebrionidae) is a tropical species used for human consumption and as an ingredient in animal feed. We investigated the hatching characteristics of Z. atratus eggs under varying conditions to optimize artificial rearing conditions. Overall, the average egg weight, width, and length decreased by 42.3%, 3.7%, and 10.1%, respectively, on the 6th day post-oviposition. We varied either temperature, photoperiod, illuminance, or humidity, while the other conditions remained constant. Of the four experimental temperatures—25 °C, 27 °C, 30 °C, and 33 °C–30 °C was associated with the highest hatching rate (91.0%) during days 5–7. Although other experimental conditions did not have a significant effect on hatchability, we were able to elucidate the ideal conditions for improved hatchability. For photoperiod, hatchability was the highest (84%) at 12L/12D, followed by 81.0% at 15L/9D, and 70% at 9L/15D. Among the illuminance conditions tested—600, 1800, and 3000 lx—hatchability was the highest at 1800 lx (82.3% on days 4–6). Among the relative humidity (RH) levels tested—50%, 65%, and 80%—hatchability was the highest at 65% RH (88.5% on days 5–6). Thus, the ideal conditions for maximum hatchability were 30 °C, 12L/12D, 65% RH, and 1800 lx. Under these combined conditions, the hatching rate increased by 93.6%, and the hatching time was reduced by two days.     

Survival of Lyophilized Bacillus popilliae in Soil

Survival of lyophilized vegetative Bacillus popilliae in dry soil and in soil kept in atmospheres with different relative humidities (RH) was determined. Cells survived for at least 1 year when the RH was 22% or lower, but an RH of 33% or higher reduced viability. At 33% RH, no bacteria were recovered after 5 months of storage; at 42% or above, no bacteria were recovered after 1 month of storage.     

Effect of temperature and relative humidity on the rate of development,fecundity and life table parameters of the red spider mite Oligonychus mangiferus (Rahman and Sapra) (Acari: Tetranychidae)

Studies on biology of Oligonychus mangiferus (Rahman and Sapra) at combination of eight constant temperatures and relative humidities (RHs) viz., 7.0°C with 85% RH, 10°C with 80% RH, 15.0°C with 75% RH, 23.0°C with 70% RH, 31.0°C with 65% RH, 34.0°C with 65% RH, 36.0°C with 60% RH and 40.0°C with 55% RH revealed that the optimal condition for the development of these mites are 15.0–31.0°C and 65–75% RH. The highest temperature and the lowest RH accelerated the rate of development and induced more reproduction of O. mangiferus. Its population also multiplied 30.81 times in a generation time of 27.36 days at 31.0°C and 65% RH, while the same population only increased 7.46 times in a generation time of 48.07 days at 15.0°C and 75% RH. Fecundity was highest at 31.0°C and 65% RH with 46.43 eggs per female. The highest intrinsic rate of natural increase was observed at 31.0°C as 0.125 per day.     

Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75-85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93-97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.     

湿度对木薯单爪螨Mononchellus mcgregori发育与繁殖的影响

【目的】木薯单爪螨是新入侵我国的重要检疫性害螨,主要危害木薯,也可危害橡胶。近年来,该螨种群数量迅速增多,扩散范围不断增大,目前已在海南、云南、广西、广东等重要木薯产区发生并加重危害,危害严重时可导致木薯减产40%~60%。湿度是影响木薯单爪螨发育和繁殖的重要因素之一,但有关该方面的研究较少。【方法】通过室内饲养,观察比较了不同湿度条件下木薯单爪螨发育及繁殖情况。【结果】当湿度为75%和85%时,卵孵化率均达100%,平均每雌产卵量分别达49.22和43.67粒,雌成螨寿命分别为21.00和22.00 d;当湿度为55%和95%时,卵孵化率和后代产卵量显著降低,雌成螨寿命显著缩短;当湿度为65%时,卵孵化率、平均每雌产卵量以及成螨寿命均与75%和85%湿度处理无显著差异,但其发育历期显著延长。【结论】75%和85%是木薯单爪螨发育与繁殖的适宜湿度条件。     

Post-abscission, pre-dispersal seeds of Digitalis purpurea remain in a developmental state that is not terminated by desiccation ex planta

Background and Aims

Seed quality may be compromised if seeds are harvested before natural dispersal (shedding). It has been shown previously that slow or delayed drying can increase potential quality compared with immediate rapid drying. This study set out to investigate whether or not there is a critical moisture content, below which drying terminates maturation events for seeds harvested after mass maturity but before dispersal.

Methods

Seeds of foxglove (Digitalis purpurea) in the post-abscission pre-dispersal phase were held at between 15 and 95 % RH for 4 or 8 d, with or without re-hydration to 95 % RH for a further 4 d, before drying to equilibrium at 15 % RH. In addition, dry seeds were primed for 48 h at −1 MPa. Subsequent seed longevity was assessed at 60 % RH and 45 °C.

Key Results

Rate of germination and longevity were improved by holding seeds at a wide range of humidities after harvest. Longevity was further improved by re-hydration at 95 % RH. Priming improved the longevity of the seeds dried immediately after harvest, but not of those first held at 95 % RH for 8 d prior to drying.

Conclusions

Maturation continued ex planta in these post-abscission, pre-dispersal seeds of D. purpurea dried at 15–80 % RH at a rate correlated positively with RH (cf. ageing of mature seeds). Subsequent re-hydration at 95 % RH enabled a further improvement in quality. Priming seeds initially stored air-dry for 3 months also allowed maturation events to resume. However, once individual seeds within the population had reached maximum longevity, priming had a negative impact on their subsequent survival.Key words: Digitalis purpurea, seed development, post-harvest treatment, priming, longevity, ex situ conservation     

Biochemical and physiological studies of certain ticks (Ixodoidea): effects of relative humidity and starvation on the water balance and behavior of adult Argas (Persicargas) arboreus (Argasidae).

The effects of high (96%) and low (0%) relative humidities (RH) and starvation on the total body weight, water content, dry weight content, and humidity responses of unfed adult Argas (Persicargas) arboreus (Argasidae) were determined each 15 days for a period of 105 days. High RH caused an increase of 6.7% in females and 7.2% in males of total body weight after 15 days followed by very slow decrease reaching 4.5% in females and 5.4% in males of initial body weight after 105 days. Low RH caused continuous decrease to 46.2% in females and 53.7% in males of the initial body weight after 105 days. After 105-day starvation at 96% RH, the initial value of the water content increased by 3% in females and 5% in males; at 0% RH this value decreased by 52% in females and 59% in males. The initial value of the dry weight content decreased by 23% in females and 26% in males at 96% RH and by 33% in females and 43% in males at 0% RH. Newly molted adults were hygronegative and at 96% RH remained so. At 0% RH, the hygronegative reaction gradually decreased and changed to hygropositive after 60 days in females and 90 days in males. Survival of 80 control ticks after 105 days was 96% at 96% RH and 54% at 0% RH.     

Effects of varying the level of palm oil on feed intake, milk yield and composition and postpartum weight changes of Red Sokoto goats

Twenty-five pregnant Red Sokoto goats (average liveweight, 33.14 ± 1.75 kg) were used from the last month of pregnancy until 118 day of lactation to evaluate the effect of varying the level of palm (Elaeis guineensis, Jacq.) oil (PO) in concentrate supplement on lactation performance. The goats were fed one of five iso-nitrogenous (16% CP) supplements containing 0% PO (control), 4% PO, 8% PO, 12% PO or 16% PO to a basal diet of Wooly finger grass (Digitaria smutsii, Stent) hay. Average consumption of concentrate was 400 g/goat/day, representing 48% of total dry matter intake. Daily dry matter intake decreased linearly with increasing levels of palm oil. The 4% PO concentrate elicited the highest milk production and was the most cost-effective, while improving daily milk production by 29% compared with the control. Milk composition and postpartum weight changes of the goats were not significantly affected by the concentrate supplements but milk fat percent was generally increased by inclusion level of palm oil in the supplement. It is concluded from this study that the concentrate supplement containing 4% palm oil can increase milk yield in Red Sokoto goats without adversely affecting dry matter intake.     

A high-performance humidity control system for tiny animals: demonstration of its usefulness in testing egg hatchability of the two-spotted spider mite, Tetranychus urticae

We developed a computer-based system for controlling water vapor conditions (i.e., humidity) using a two-flow method in which streams of humidified and dehumidified air were combined in an acrylic container. The flow rate of each stream was independently controlled to adjust relative humidity (RH). In this system, humidification from 15 to 90?% RH and dehumidification from 90 to 15?% RH at an air temperature (AT) of 25?°C were properly operated with short time constants of 4.3 and 10?min, respectively. Tetranychus urticae egg hatchability was then examined at 20-95?% RH and 25?°C AT. The coefficients of variation of RH were low (0.3-1.5?%). Egg hatchability in a polystyrene Petri dish was lower at 20?% RH than at 70-95?% RH. A delay in hatching was also observed at 70?% RH for eggs tested on a leaf disk placed on water-soaked cotton; this delay was attributed to the AT being 1.4?°C lower on the leaf surface than on the inner surface of the dish. Our system is expected to be useful for further examination of ecological and behavioral responses in pest mites and for developing novel physical control measures using water vapor.     

Effects of fluctuating moisture and temperature regimes on the persistence of quiescent conidia of Isaria fumosorosea

Conidia of Isaria fumosorosea were submitted to three regimes of temperature and moisture to simulate microclimatic conditions which prevail in temperate (43% RH and 28 °C to 98% RH and 15 °C), subtropical (75% RH and 35 °C to 98% RH and 25 °C), and arid areas (13% RH and 40 °C to 33% RH and 15 °C) with daily fluctuating cycles. Germination, conidial viability, and virulence to Spodoptera frugiperda larvae were less affected after 20 days exposure under temperate cycling conditions than under arid and subtropical conditions. Exposure of conidia for 20 days to constant nocturnal simulated conditions of any tested regime weakly affected conidial persistence, whereas diurnal conditions exerted the most detrimental effects of high temperatures. However, when tested at both 45 °C and 50 °C at 33% RH for 160 h, the persistence of I. fumosorosea conidia was relatively higher than expected. These results emphasize that climatic conditions prevailing in environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies.     

The effect of stored barley cultivars, temperature and humidity on population increase of Acarus siro, Lepidoglyphus destructor and Tyrophagus putrescentiae

The rate of population increase of three mite species, Acarus siro (L.), Lepidoglyphus destructor (Schrank) and Tyrophagus putrescentiae (Schrank), was studied on various types of barley and at various combinations of temperature and humidity. The mites were added into the chambers and incubated for 21 days on seven different kinds of barley coming from four sites, including six cultivars and a mixture. The population increase of all species was higher on the mixture than on any other cultivar, except for Sebastian and Calgary. The increase of mites was studied at constant temperatures ranging from 5 to 35 °C and relative humidity (RH) ranging from 50 to 90 %. Positive rate of increase was found above 70 % RH for all species. The optimal humidity was at 85 % RH for A. siro and L. destructor and at 90 % RH for T. putrescentiae. As concerns the temperature, positive rate of increase was found at temperatures higher than 10, 15 and 20 °C for A. siro, L. destructor and T. putrescentiae, respectively. The temperature optima were at 23, 25, and 30 °C for A. siro, L. destructor and T. putrescentiae, respectively. Model estimated on laboratory data was then fitted to temperature and humidity records from August to November in the Czech grain store. Estimated population rate of increase was rarely positive: for A. siro it was for 24 %, for L. destructor for only 1 % and for T. putrescentiae for only 7 % days of the study period. It is concluded that in the climatic conditions of the Czech Republic the population increase of three mite pests is negligible during autumn and winter.     

汽爆葛根直接固态发酵乙醇联产葛根黄酮

针对葛根原料富含纤维和黄酮等特点, 选用低压汽爆处理代替糊化直接固态同步糖化发酵乙醇, 而后提取发酵剩余物的葛根黄酮。实验结果表明鲜葛根在0.8 MPa压力下维持3.5 min汽爆处理后, 直接加入糖化酶(65 u/g)、纤维素酶(1.5 u/g), 0.1%(NH4)2SO4、0.1%KH2PO4和活化后的酵母, 35~37oC下, 固态同步糖化发酵60 h, 100 g干葛根可生产的乙醇与葛根黄酮分别为27.47 g、4.43 g, 淀粉利用率达到95%。该方法实现了葛根分层多级转化清洁利用, 为非粮食类淀粉资源发酵乙醇提供了一条新途径。     

Moisture content of the dried leaf is critical to desiccation tolerance in detached leaves of the resurrection plant Boea hygroscopica

In our experimental conditions detached leaves of the resurrection plant Boea hygroscopica survived equilibration to 65–80% RH (Relative Humidity), but not to very low RH (close to 0%). The first aim of our research was to determine whether sensitivity to equilibration to very low RH depends on the rate of the drying process or on the very low final MC (Moisture Content) attained. The second aim of our research was to determine ABA content of leaves exposed to the two drying processes: a first step towards understanding whether ABA is involved in the tolerance mechanism of Boea hygroscopica.Detached leaves were equilibrated either to 1.4 or to 60–70% RH or to various temporal combinations of these two RH. ABA content was monitored during drying. Dehydrated leaves were imbibed in liquid water either directly or after a slow rehydration at 98% RH. Tolerance was assessed after 48 h imbibition in liquid water.The low final MC attained (about 3%) and not the rate of drying was responsible of the sensitivity of leaves equilibrated to 1.4% RH. Slow rehydration attained better recovery, but it was not able to allow full resurrection thus suggesting that a plain biophysical liquid-crystalline to gel phase transition of the membrane lipid bilayer could not fully account for the lethal damage of the very low MC.The conclusions relative to the first part of our research was of primary importance in interpreting results concerning ABA variations during the two drying treatments. ABA showed a very similar transient increase when excised leaves were dried at either 1.4% RH (sensitive leaves) or at 60–70% RH (tolerant leaves). However we cannot exclude that the transient increase of the hormone is a necessary component of the desiccation tolerance mechanisms in detached leaves of Boea hygroscopica: the extremely low MC reached by equilibration to 1.4% RH may impair the mechanism itself.