Rice (Orzya sativa L.) shows a similar temperature response to maize because pollen viability and production declines as daytime maximum temperature (Tmax) exceeds 33 °C and ceases when Tmax exceeds 40 °C.
Reasons of Crop Yield last year in Monsoon
The main causes of rice and maize crop failure in the following year is due to,
- Failure of proper pollination and sterilization of pollens
- Temperature fluctuations
1. Failure of proper pollination and sterilization of pollens
Pollination in Maize:
- Pollen shed or anthesis is controlled by a combination of genetic and environmental factors.
- Once pollen grains have matured inside corn anthers, these anthers begin to dry or dehisce.
- Anthers typically shed pollen around midmorning as anthers dry in the heat and sunlight.
- As anthers dehisce, they split apart to allow pollen grains to fall into the open air.
- Pollen grains are viable for only a few minutes after they are shed until they desiccate.
- A tassel normally sheds pollen for about 5 days.
- Pollen shed in a field can last up to 2 weeks.
- Each silk that emerges from an ear shoot connects to a single ovule, or potential kernel.
- A silk must be pollinated for the ovule to develop into a kernel.
- Silk emergence proceeds from the base to the tip of the ear over the course of 4 to 8 days.
- Silks will continue to elongate for up to 10 days after emergence or until they are pollinated.
- Silk receptivity decreases over time following emergence due to the senescence of silk tissue.
Drought Effects on Silk Growth:
- Reduction in kernel number may result from asynchrony of pollen shed and silking.
- Silk elongation requires high water potential ― drought stress can delay silking and increase the anthesis-silking interval (ASI) ― the time between the start of pollen shed and silk emergence.
- Silks that emerge after most of the pollen is shed may not be pollinated.
- Moderate silk delay can cause poorly filled ear tips, whereas more severe stress can result in ears that are nearly or completely barren.
Heat Effects on Pollen Shed:
- The location of the tassel exposes it to high radiation and potential temperature extremes.
- Extreme heat stress (over 100 F) can reduce pollen production and viability.
- Severe losses in pollen production or viability are necessary to affect kernel set, which would require an extended period of extremely high temperatures
- Drought stress can prevent pollination, as well as cause successfully pollinated kernels to abort.
- Drought stress causes kernel abortion by reducing photosynthesis and carbohydrate availability following pollination.
- Insects such as corn rootworm beetles and Japanese beetles can interfere with pollination by clipping silks.
- Clipped silks can still elongate and receive pollen; however continuous intense insect activity can result in reduced seed set.
The temperature during pollen development has also been shown to affect the chemical composition of pollen and some aspects of pollen performance Pollen collected from the three types of plants growing in the cool and hot chambers was germinated in vitro and pollen tube lengths were measured. Analysis revealed significant effects of plant type and germination temperature on pollen tube growth. Moreover, the pollen tubes from the plants in the cool chamber grew longer than the pollen tubes from the plants in the hot chamber. Furthermore, results from a crossing experiment showed that plants grown in cool conditions sired more seeds than the ones that developed in hot conditions. This study indicates that the temperature during pollen development has the potential to influence fitness through male function.
A study that examined more realistic temperature variations (i.e. not constant) under field conditions was performed on Silene acaulis, a long-lived cushion plant that is circumpolar in the northern hemisphere, occurring in arctic and alpine tundra. Soil temperature during flower development was altered by placing one-meter diameter shields of reflecting material (aluminized mylar) around S. acaulis plants, with a hole cut out for the actual cushion. These shields reflected the sunlight and lowered soil temperature in the root zone by just over 18C. Crosses with pollen from these plants revealed that pollen tubes from cold-stressed donors were significantly shorter than pollen tubes from nearby control donors. These results indicate that relatively cold root temperatures experienced during the time of flower maturation that are nonetheless well within the range of natural temperature variation had an effect on pollen tube growth rates.
2. Temperature extremes in climate:
One of the more susceptible phenological stages to high temperatures is the pollination stage. Maize pollen viability decreases with exposure to temperatures above 35 °C. The effect of temperature is enhanced under high vapor pressure deficits because pollen viability (prior to silk reception) is a function of pollen moisture content which is strongly dependent on vapor pressure deficit. During the endosperm division phase, as temperatures increased to 35 °C from 30 °C the potential kernel growth rate was reduced along with final kernel size, even after the plants were returned to 30 °C. Exposure to temperatures above 30 °C damaged cell division and amyloplast replication in maize kernels which reduced the size of the grain sink and ultimately yield.
Rice (Orzya sativa L.) shows a similar temperature response to maize because pollen viability and production declines as daytime maximum temperature (Tmax) exceeds 33 °C and ceases when Tmax exceeds 40 °C. Current cultivars of rice flower near mid-day which makes Tmax a good indicator of heat-stress on spikelet sterility. These exposure times occur quickly after anthesis and exposure to temperatures above 33 °C within 1−3 h after anthesis (dehiscence of the anther, shedding of pollen, germination of pollen grains on stigma, and elongation of pollen tubes) cause negative impacts on reproduction. Current observations in rice reveal that anthesis occurs between about 9 to 11 am in rice and exposure to high temperatures may already be occurring and will increase in the future. There is emerging evidence that differences exist among rice cultivars for flowering times during the day. Given the negative impacts of high temperatures on pollen viability, recent observations from suggest flowering at cooler times of the day would be beneficial to rice grown in warm environments. They proposed that variation in flowering times during the day would be a valuable phenotypic marker for high-temperature tolerance. Crop sensitivity to temperature extremes depends upon the length of anthesis.
As we know that we don’t change the climatic pattern, one and only way to solve this problem is to make zone of crops according to climate and area suitable for that crop.
- First, they must be able to develop superior maize and rice varieties and hybrids which tolerate the climatic harshness of Pakistan and generate high-yielding technologies that are appropriate in typical farming systems.
- Sowing of maize and rice varieties are must be done at their recommended date according to area.