Maximum Pollen Tube Length Research Articles

Effects of temperatures on pollen germination and pollen tube growth in apple

Apple cultivars in Korea have been experiencing poor fruit sets due to early spring low temperatures and global warming. Therefore, the present study aimed to investigate the effects of temperature on fruit setting and to select apple cultivars tolerant to extreme temperatures based on the temperature response of their pollen. The effect of temperature on pollen germination percentage (PGP) and on pollen tube length (PTL) was determined under laboratory conditions using the pollen of ten apple cultivars. The two parameters were evaluated using a pollen germination medium, at temperatures ranging from 5 to 45 °C, at 5 °C intervals. The temperature variations considerably affected pollen germination and tube growth in all the examined cultivars. The maximum pollen germination percentage ranged from 61.5 (“Green Ball”) to 99.9% (“Shinano Gold”) with a mean of 85.2%, whereas the maximum pollen tube length ranged from 716.5 (“Tsugaru”) to 989.8 µm (“Arisoo”) with mean of 855.1 µm. There were differences in the cardinal temperatures (Tmin, Topt, and Tmax) of PGP and PTL between cultivars. Mean cardinal temperatures Tmin, Topt, and Tmax computed using the modified bilinear model were 4, 27.7, and 44.9 °C and 6.3, 28.6, and 43.7 °C for PGP and PTL, respectively. Our preliminary results may be used to select low-temperature and global warming-friendly apple cultivars for farmers and can also be exploited to develop temperature-tolerant apple cultivars during flowering.

Pollination biology of Pongamia pinnata (L.) Pierre: a potential biodiesel plant

Pongamia pinnata, is an important biodiesel plant in India. The seed is an economic part of the plant used for extraction of biodiesel. The reproductive biology of P. pinnata is important for determining barriers in setting pods. The study has been carried out at Central Agroforestry Research Institute, Jhansi, India, during 2017–2019. The observations were made on the floral biology and pollinator activity in P. pinnata for 2 years. Anthesis was noticed between 0800 and 1000 h with peak anthesis between 0800 and 0830 h. Flower longevity was only 1 day. Pollen dehiscence occurred 1–2 h before anthesis. Pollen remained viable throughout the day with maximum germination (96.15%) coinciding anthesis time. Whereas, maximum pollen tube length (0.54 ± 0.10) was observed during 1000 h. Stigma remained receptive for 8 h after anthesis, the maximum receptivity was noticed 2 h after anthesis (82% of pollen germination) and it was coinciding the time where maximum pollen tube length recorded. The style was longer than stamens, indicating that the flower appeared to be adapted for cross-pollination. There were 13 flower visitors recorded, of which Megachile species were more abundant compared to Apis, Xylocopa species and, other flower visitors. The pollinator exclusion experiment was conducted to assess the role of flower visitors on pollination and fruit set. No pod set was noticed in the absence of insect pollinators. Whereas, in an open-pollinated condition, pod set ranged between 15 to 18%.

Effect of temperature on pollen germination for several Rosaceae species: influence of freezing conservation time on germination patterns.

Between February 2018 and April 2018, flowers were collected from eight Rosaceae species. Flowers were kept in a freezer at −20 °C for three freezing times (Treatment 1, two months; Treatment 2, four months; Treatment 3, six months). After extracting pollen, in vitro germination was induced in a culture medium and incubated at six different temperatures for 72 h. The percentage of pollen germination, average pollen tube length and maximum pollen tube length were measured. Pollen germination was maximum for all species between 15 °C and 30 °C. Cydonia oblonga, Malus sylvestris, Prunus avium, Prunus domestica, Prunus dulcis, Prunus persica and Pyrus communis obtained 30–52% pollen germination between 15 °C and 20 °C. Prunus cerasifera had 40% pollen germination at 30 °C. All species studied reached the maximum pollen tube length between 10 °C and 25 °C. Germination did not change significantly for any of the species with freezing time, but we found significant differences in the three parameters measured between treatments. The highest germination percentages were obtained in Treatment 2 (four months frozen at −20 °C), while the maximum pollen tube length was reached in Treatment 1 (two months frozen at −20 °C). According to our results, freezing time affected the germination-temperature patterns. This could indicate that studies on the effect of temperature on pollen germination should always be carried out with fresh pollen to obtain more conclusive data.

Study of pollen morphology and salinity effect on the pollen grains of four olive (Olea europaea) cultivars

Pollen and seed germination tests can be used as effective test in screeing salt-tolerant crop and pollen grain morphology characteristics can be used to determine interspecific and intraspecific relationships among olive species. So, This study was conducted to investigate the effect of different salinity concentrations on pollen germination, tube growth and further evaluation of pollen grain morphological characteristics using Scanning Electron Microscopy (SEM) of four olive (Dezful, Mission, Koroneiki and Tarom2) cultivars. Results showed that polar axis (P), equatorial axis (E), and the distance between furrow edges and ridges width were significantly different between four olive cultivars. The value of polar axis ranged from 18.77 μm in ‘Koroneiki’ up to 20.03 μm in ‘Dezful’, while the mean values of equatorial axis ranged from 12.76 μm for ‘Tarom2’ up to 13.68 μm for ‘Dezful’. The lowest distance between furrow edges (12.13 μm) and width of ridges (8.63 μm) were obtained in ‘Mission’ cultivar. It indicated that ‘Dezful’ and ‘Mission’ olive cultivars produced pollen grains with low mesh density in unit area and incomplete closure. While, ‘Tarom2’ and ‘Koroneiki’ produced pollen grains with high mesh density and complete closure. The results also elucidated that the amount of pollen germination decreased as concentration of salinity increased on the medium. The reduction of pllen germination rate occurred at the 83.71%, 96.68%, 86.83% and 87.38% with additional of 25 mM NaCl in the media of ‘Tarom2’, ‘Dezful’, ‘Mission’ and ‘Koroneiki’ cultivars, respectively. The maximum pollen tube length (171.99 μm) was observed in ‘Tarom2’ cultivar cultured in a salinity-free medium; while pollen tube length was the lowest (3.5 μm) in ‘Dezful’ cultivar cultured in a medium containing 25 mM of NaCl. Findings also revealed information in which was able to categorize cultivars into tolerant (‘Tarom2’), semi-tolerant (‘Mission’ and ‘Koroneiki’) and sensitive (‘Dezful’) based on tolerating critical salinity (lethal salinity) condition at the pollen germination stage. According to the results of this experiment, it can be concluded that investigate the effect of salinity stresses on gametophytic phase could be applied for the screening tolerant olive cultivars to salt stresses.

Heat tolerance evaluation in commercial African violet cultivars using physiological and pollen parameters

High temperatures negatively affect the vegetative and reproductive growth of African violets thus decreasing their aesthetic and commercial values. No scientific information is currently available on cultivar tolerance to high temperatures in this plant. This study was conducted with the objective of evaluating heat tolerance in commercial African violet cultivars using a combination of physiological and pollen parameters and ranking the cultivars based on their cumulative temperature response index (CTRI). Physiological parameters including cell membrane thermostability (CMT), canopy temperature depression (CTD) and chlorophyll stability index (CSI) were analyzed using fully expanded leaves. In vitro pollen germination percentage (PG) and pollen tube length (PTL) were estimated at between 10 and 40°C. Cardinal temperatures (Tmin, Topt, and Tmax) of PG and PTL, as well as maximum PG percentage (PGmax) and maximum PTL (PTLmax), were estimated using the modified bilinear model. Results showed the different cultivars varied significantly for their CMT (5.39–74.07%), CTD (−1.65 to 0.61°C) and CSI (70.16–81.06%). They also differed for PG (mean of 54.43%), PTL (mean of 3109.08μm), and cardinal temperatures (Tmin=−2.5°C, Topt=24.9°C, and Tmax=49.9°C for PG; Tmin=3.4°C, Topt=26.0°C, and Tmax=43.1°C for PTL). The CTRI of each cultivar was calculated as the sum of individual stress response index (ISRI) derived from CMT, CTD, CSI, and PGmax, PTLmax, Tmin, Topt, and Tmax for PG and PTL. Among the thirty cultivars screened, the cultivars ‘Rob's Ooey Gooey’ and ‘Mac's Stop Sign’ had high CTRI values for the physiological and pollen parameters, singly or in combination, so are potential candidates to be used for the development of novel heat tolerant genotypes.

Assessment of Pollen Viability, Germination, and Tube Growth in Eight Tunisian Caprifig (Ficus caricaL.) Cultivars

The evaluation of pollen viability and its germination capacity are two essential criteria for pollinator’s characterization. This study was carried out to evaluate pollen quality of eight caprifigs grown in the center-east and north-west of Tunisia. Two colorimetric tests 2,3,5-triphenyl tetrazolium chloride (TTC) and acetocarmine were used to estimate pollen viability. Germination rate and pollen tube growth in a culture medium containing 5% sucrose, 5 ppm boric acid (H3BO3) and 1% agar were registered after 24, 48, and 72 hours (H) of incubation. Results showed that the highest pollen viability rate (84%) was obtained by TTC test in caprifig Assafri, followed by Jrani (80.2%), Djebba 2 (77.8%), and Djebba 1 (73.6%). That of other caprifigs did not exceed 50% for the two tests. In all caprifig types, germination rate and pollen tube growth varied according to the incubation period. The highest percentage of germination (72%) and maximum pollen tube length (960 μm) were recorded after 72 H of incubation in caprifigs Assafri and Jrani, respectively. Among the caprifigs studied, four types (Assafri, Jrani, Djebba 1, and Djebba 2) appeared to be suitable pollinators with respect to the criteria investigated.

Influence of temperature on the in vitro pollen germination and pollen tube growth of various native Iranian almonds (Prunus L. spp.) species

Pollen germination and pollen tube growth was quantified among various native Iranian wild almonds (P. dulcis (Mill.) D. A. Webb, P. eleaegnifolia Mill., P. orientalis Mill., P. lycioides Spach, P. reuteri Bioss. et Bushe, P. arabica Olivier, P. glauca Browick and P. scoparia Spach in order to identify differences in the tolerance of pollen to temperature variations. Pollen germination and pollen tube growth were observed after incubation in darkness in a germination medium for 24 h at 10–50°C at 5°C intervals. Maximum pollen germination of the wild almond species and specify that 60% was obtained for P. orientalis pollen and 98% for P. scoparia. Pollen tube length ranged from 860 μm was obtained in P. lycioides and 1490 μm in P. scoparia. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Almond species variation was found for cardinal temperatures (Tmin, Topt and Tmax) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures averaged over eight almond species were 14.7, 24.2, and 43.7°C for maximum percentage pollen germination and 14.48, 25.3, and 44.4 °C for maximum pollen tube length. The principal component analysis (PCA) identified maximum percentage pollen germination and pollen tube length of the species, and Tmax for the two processes as the most important pollen parameters in describing a species tolerance to high temperature. PCA also classified Prunus L. spp. into four groups according to the tolerance of pollen to temperature variations. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating species for high temperature tolerance.

The effects of temperature on in vitro pollen germination and pollen tube growth of Pistacia spp.

The pollen germination and pollen tube growth among nine Pistacia genotypes was quantified in order to identify differences in the tolerance of pollen to temperature variations. The effect of temperature on in vitro pollen germination and pollen tube growth was investigated in Pistacia vera (Uygur, Atli, Kaska, Sengel, Kavak), P. atlantica, P. khinjuk, P. terebinthus and P. palaestina. When pollen was incubated in a germination medium for 24 h in darkness, distinct differences were observed in pollen germination and pollen tube growth at different temperatures. Pollen was collected at anther dehiscence and was exposed to temperatures from 5 to 40 °C at 5 °C intervals. There were some differences between the percentage of pollen germination and pollen tube growth at different temperatures. Pistacia species and cultivars were found to range from most tolerant to most susceptible, depending on pollen characters. Pollen germination of the genotypes ranged from 83% to 97% and pollen tube length ranged from 697 to 1270 μm. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Genotype variation was found for cardinal temperatures ( T min, T opt and T max) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures averaged over nine genotypes were 6.7, 23.9 and 41.1 °C for maximum percentage pollen germination and 6.4, 23.9 and 39.8 °C for maximum pollen tube length.

Screening Capsicum species of different origins for high temperature tolerance by in vitro pollen germination and pollen tube length

Successful fruit set depends on several reproductive processes including pollen germination and tube growth processes. An experiment was conducted to determine the effects of temperature on pollen germination characteristics and to identify species/genotypic differences in Capsicum using the cumulative temperature response index (CTRI) concept. Pollen was collected from plants of seven genotypes from five Capsicum species, adapted to various parts of the world and grown outdoors in large pots. The pollen was subjected to in vitro temperatures ranging from 15 to 50 °C at 5 °C intervals. Pollen germination and tube lengths were recorded for all species after 24 h of incubation at the respective treatments. Species/genotypes differed significantly for in vitro pollen germination percentage and pollen tube length with mean values of 78% and 734 μm, respectively. The mean cardinal temperatures ( T min , T opt , and T max ) averaged over genotypes, were 15.2, 30.7, and 41.8 °C for pollen germination and 12.2, 31.2, and 40.4 °C for pollen tube growth. The CTRI of each species/genotype calculated as the sum of eight relative individual stress response values, such as maximum pollen germination, maximum pollen tube length; T min , T opt , and T max temperatures of pollen germination, and pollen tube lengths, identified species tolerance to high temperatures. Capsicum annum cv. Mex Serrano from Mexico was identified as tolerant, C. chacoense cv. 1312 and C. spp. cv. Cobanero from Argentina and Guatemala, respectively as intermediate and C. frutescens cv. Early Spring Giant from China, C. annum cv. Long Green from South Korea , C. spp. cv. NM89C130 and C. pubescens cv. 90002 from Guatemala as sensitive to high temperatures. The tolerant species/genotypes can be used in breeding programs to develop new genotypes that can withstand high temperature conditions both in the present climate and particularly in a future warmer climate.

Pollen‐Based Screening of Soybean Genotypes for High Temperatures

ABSTRACTSoybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures > 35°C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50°C at 5°C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 μm). Mean cardinal temperatures (Tmin, Topt, and Tmax) were 13.2, 30.2, and 47.2°C for PG and 12.1, 36.1, and 47.0°C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum (Tmax), minimum (Tmin), and optimum (Topt) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat‐tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30°C) compared with heat‐intermediate (PI 471938) and heat‐sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumellae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88‐5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [CO2] did not modify reproductive parameters or CTRI. The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature‐tolerant genotypes and temperature‐dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.

Screening for High‐Temperature Tolerant Cotton Cultivars by Testing In Vitro Pollen Germination, Pollen Tube Growth and Boll Retention

AbstractWith radical global climate change and global warming, high temperature stress has become one of major factors exerting a major influence on crop production. In the cotton (Gossypium hirsutum L.)‐growing areas of China, especially in the Yangtze River valley, unexpected periodic episodes of extreme heat stress usually occur in July and August, the peak time of cotton flowering and boll loading, resulting in lower boll set and lint yield. Breeding programs for screening high temperature‐tolerant cotton germplasm and cultivars are urgent in order to stabilize yield in the current and future warmer weather conditions. In the present study, 14 cotton cultivars were quantified for in vitro pollen germination and pollen tube growth in response to temperatures ranging from 10 to 50 °C at 5 °C intervals. Different cotton genotypes varied in their in vitro pollen germination and pollen tube length responses to the different temperatures. Maximum pollen germination and pollen tube length ranged from 25.2% to 56.2% and from 414 to 682 μm, respectively. The average cardinal temperatures (Tmin, Topt, and Tmax) also varied among the 14 cultivars and were 11.8, 27.3, and 42.7 °C for pollen germination and 11.8, 27.8, and 44.1 °C for maximum pollen tube length. Variations in boll retention and boll numbers per plant in field experiments were found for the 14 cotton cultivars and the boll retention and boll retained per plant on 20 August varied considerably in different years according to weather conditions. Boll retention on 20 August was highly correlated with maximum pollen germination (R2= 0.84) and pollen tube length (R2=0.64). A screening method based on principle component analysis of the combination of pollen characteristics in an in vitro experiment and boll retention testing in the field environment was used in the present study and, as a result, the 14 cotton cultivars could be classified as tolerant, moderately tolerant, moderately susceptible and susceptible to high temperature.(Managing editor: Li‐Hui Zhao)

Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature

AbstractAir temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (Tmin, Topt and Tmax) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and Tmax for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related (R2 = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.