hamidreza khazaee

The effects of temperature increases on the growth of tomato fields are among the obvious results of global warming and are considered an important issue that should be investigated. To maintain and develop the cultivation systems of this crop, a proper understanding of the heat tolerance mechanisms and physiological responses in tomatoes should be achieved. The primary objective of this research is to discover the impact of heat stress on the germination and growth of pollen grains in research tomato germplasms. The researchers' knowledge about the response of different tomato cultivars to abiotic stresses is limited and only the effects of enzymes involved in the response process, heat shock proteins and some hormones have been investigated. The process of detecting heat stress-sensitive stages and their enhancement is facilitated by having a correct understanding of physiological processes.

The seeds of heat-resistant (LA2661 and LA2662) and -sensitive (LA3911) research cultivars of tomato were used to evaluate the effects of increasing day and night temperatures. The obtained seedlings were grown under optimal temperature conditions (24°C day/18°C night), and after observing the first flower primordium, were incubated in growth chambers to apply daytime heat stress treatments, including temperatures of 28°C, 32°C and 36°C day/18°C night and night stress treatments including temperatures of 28°C, 32°C, and 36°C at night/ 24°C day for 7 days. Pollen grains were then evaluated for their survival, germination, and growth.

The findings of the daytime heat stress tests show that the percentage of survival and germination of pollen grains and growth of pollen tubes of cultivars LA2661, LA2662 and LA3911 decreased as daytime temperature rose from 24 °C to 36 °C. This reduction is more noticeable for the sensitive cultivar LA3911. Degraded pollen grains increased in the LA3911 cultivar due to heat stress. The survival percentage of pollen grains in all three studied cultivars decreased due to the application of heat stress at night. The resistant cultivars LA2661 and LA2662 had a higher germination percentage compared to the sensitive cultivar LA3911. Pollen grains germination decreased by 50% as a result of increasing the night temperature from 18°C to 36°C. Pollen tube length was reduced in both cultivars and night treatments.

The effects of heat stress in the early stages of flowering when flowers are visible are high, and reproductive stages are very sensitive to high temperatures and affect fertility and processes after insemination, and finally, they lead to yield loss. The daytime temperature increase relative to the natural temperature range (22°C to 24°C) during growth severely impacts the number of pollen grains released from tomato flowers. The number of non-living pollen grains is higher at 36°C day and 32°C and 36°C night temperatures compared to optimal temperature conditions. It appears that the increase in nighttime temperature results in more severe consequences than the increase in daytime temperature.

Currently, the most important selection criterion for drought tolerance in wheat breeding programs is to compare grain yields between wheat cultivars grown under normal and deficit irrigation conditions. Several reports indicate that wheat traits, such as grain yield, biomass and yield components are decreased when the crop encounters water stress (Mohseni and Akbari, 2012). Heritability for yield is low under drought conditions due to high interaction between genotype and environment or low genetic variation. For this reason, secondary characteristics such as physiological traits have been given particular attention for selection process by researchers. Leaf relative water content (LRWC), chlorophyll content, water use efficiency (WUE), proline and abscisic acid accumulation are of some physiological indices as a measure for selection of drought tolerant cultivars. LRWC is considered as a screening tool under drought condition. (Blum et al., 1981). LRWC is affected by osmotic pressure, water uptake and respiration rate and shows a high heritability under drought conditions. Crop chlorophyll (Chl) content decreases under drought conditions and plants with high Chl content are more tolerant to drought (Abdoli et al., 2013). In crops with high chlorophyll content, photosynthesis activity continues under drought conditions. Thus the experiment was conducted to investigate the effect of limited irrigation on some morphological and physiological traits of bread and durum wheat under Mashhad-Iran environmental conditions The study was conducted at experimental field of Ferdowsi university of Mashhad during 2011 and 2012 growing seasons in order to evaluate the effect of limited irrigation on yield and physiological characteristics of wheat. A split plot experiment based on randomized complete block design with three replications was performed. The main plots were assigned to irrigation levels including (I1)100, (I2)75, (I3)50 and (I4) 25 percent of evaporation from evaporation pan class A and the sub-plots consisted of wheat cultivars (three hexaploid cultivars (Pishgam, Alvand, Erum) and three durum cultivars (Behrang, Arya, Dena). Land preparation was done on late October according to farmers practice in the area. There were six 3m long rows spaced 20cm apart in each plot. The studied characteristics were yield component traits, flag leaf chlorophyll content, chlorophyll (Chl) a, and b contents and flag leaf relative water content (LRWC). The results of analysis of variance showed that there was significant difference between cultivars in terms of grain yield. Also, grain yield was significantly affected by irrigation levels but was not affected by interaction between the treatments. The highest (723 kg/m2) and lowest (677 kg/m2) grain yields were produced by Pishgam and Alvand cultivars respectively. The highest (52%) and lowest (32%) harvest index were observed for Dena and Erum cultivars, respectively. There was no significant difference between irrigation levels for harvest index. There was no significant difference between cultivars for chlorophyll content There was a significant difference between cultivars for chlorophyll a content. The highest chlorophyll a content (2.49 mg/g fresh weight) was observed for Dena cultivar. There was significant difference between irrigation levels for chlorophyll a and b contents. Chlorophyll content was significantly affected by irrigation level and chlorophyll a and b concentrations were decreased by water deficit. There was no significant difference under normal irrigation levels between chlorophyll content index and the Chl a, and b concentrations. LRWC was different with different cultivars and was affected by irrigation levels. The highest and lowest LRWC were obtained with Pishgam and Alvand cultivars, respectively. There was no significant difference between the other cultivars for LRWC . The highest grain yield was obtained from Pishgam and Alvand cultivars. The former and the latter gave the highest yield because of higher 1000-grain weight and higher numbers of grain per spike, respectively. Harvest index of all the wheat cultivars remained stable and was not affected by water stress. Water stress reduced LRWC, chlorophyll index content and chlorophyll a and b concentrations. The reduced chlorophyll content led to diminished production of photosynthates, resulting in decreased grain yield and biomass in the all cultivars. Since selection based on grain yield is not useful because of its low heritability, LRWC can be used as the selection criterion for cultivars with high yield performance under water deficit conditions.

In order to compare the effect of irrigation levels and methods on leaf area and replacement corm production of saffron during 2013-2014 growing season, a split plot experiment was conducted in randomized complete block design with three replications in the Jolgeh Rokh District, in 35 km Torbat Heydarie. The main plot basin irrigation, drip and sprinkler irrigation and sub plot was three levels of irrigation (100, 75 and 50 percent water requirement of saffron). The traits studied were including dry weight, number, diameter and length of leaf, dry weight, size and number of replacement corms, weight and length sheath. Sampling for determining the characteristics of leaf and sheath was done on April 30, and for corm it was done on May 31, 2014. The results showed that in the irrigation method treatments, the most dry weight of corm, leaf and sheath weight, size and number of replacement corm, number, diameter and length of leaf were observed in the case of drip irrigation. In addition, the best yield was observed in drip irrigation and the lowest amount was seen in basin irrigation. Saffron irrigation with the drip method resulted in an increase of the number of replacement corms compared to the sprinkler and basin methods (10 and 34 percent, respectively). The effect of irrigation levels was significant on some of the traits that were studied and the most yield was related to 100 percent irrigation level and the lowest one was in the 50 percent water requirement. Reducing irrigation from 100 to 50% crop water requirement severely reduced replacement corms number and their weight (62 and 86 percent, respectively). Consequently, the most photosynthesis level of Saffron and also the maximum amount of total number and total weight of replacement corms were obtained in the drip irrigation case and 100 percent irrigation level