Study on the Agroclimatic Division of Thermosensitive Genetic Male Sterility Rice Breeding

Xiaomin CHEN,Huilin CHEN,Haiping ZOU,Bin WANG

Hai’nan Institute of Meteorological Science,Haikou 570203,China

Responsible editor:Nanling WANG Responsible proofreader:Xiaoyan WU

Two-line hybrid rice not only has the remarkable advantages of simplifying the procedures of breeding and hybrid seed production,and reducing the cost of seed production,etc.,but also has the merits of making full use of conventional rice breeding achievements due to its wide restoring resources and free combination,therefore,it has received extensive attention from the country and rice breeders[1].In recent years,with the indepth study of two-line hybrid rice,rice varieties become enormous,breeding and planting area of two-line hybrid rice is expanding,the development impetus has caught up with and surpassed three-line hybrid rice.But there were some problems in widespread popularization process of two-line hybrid rice,for example,photo-thermosensitive genetic male sterility (PTGMS) was typical ecological genetic male sterility,so it was required to maintain low temperature below the initial temperature for fertility transition in a certain time in fertility sensitive period when breeding,and appropriate high temperature was required for flowering and pollination in headingflowering stage,thereby achieving high yield[2].To solve the breeding problems of thermo-sensitive genetic male sterility(TGMS)rice,the previous studies have found the following techniques,such as cold water irrigation[3-4],Hainan winter and spring breeding[5-6],high elevation regions breeding[7-9]and stem-cutting ratoon breeding[10],etc.,but in practice,only Hainan winter and spring breeding technique was used by most people[2,5-8].

Two-line hybrid rice breeding is a work with high technology,multiple links and high requirement.First,we should consider local meteorological conditions[2,11-13],especially breeding in different places,we must first collect and research meteorological data,arrange fertility sensitive period and heading-flowering period in the optimal meteorological condition.At present,anti-season breeding of two-line hybrid rice is mainly in Sanya,Lingshui,etc.By the statistics[14],in 2010,nearly 3 000 people (excluding farmers)from 502 units (or research groups) in 29 provinces (municipalities and autonomous regions) nationwide registered in Hainan National Breeding Office,to breed in Hainan Breeding Base,and the declaration area reached 3 568 hm2(except northern Hainan area).Therefore,this paper studied the climatic regionalization of Hainan hybrid rice using the meteorological data during January-March of Hainan Province,based on temperature indicators required by TGMS rice during fertility sensitive period and heading-flowering period,applying GIS technology and the regression analysis of mathematical statistics as well as refined net model analysis,to provide reasonable layout and scientific basis for sustainable development of TGMS rice in Hainan Island under the background of global warming.

Materials and Methods

Overview of the research regions

Hainan Island (18°10′-20°10′N,108°37′-111°03′E),located in the southernmost part of China,its land area is 3.39×104km2,mountains and terraces are the dominant terrain,accounting for 38.7% of areas in Hainan Island.Hainan,lies in the northern margin of the torrid zone,belongs to tropical monsoon climate,has always enjoyed the reputation of “natural greenhouse” due to its long summer without winter,the annual average temperature here is 22-26 ℃,accumulated temperature of ≥10 ℃average temperature is 8 200 ℃,even the temperature of January and February as the coldest time of the year reaches to 16-21 ℃,the annual sunshine duration is 1 750-2 650 h,and the percentage of sunshine is 50% -60%,moreover,the light and temperature are sufficient,and photosynthesis potential is high[14].

Data sources and treatments

Sequential and complete meteorological data during 1961-2010 from 18 meteorological stations of Hainan were selected,to calculate meteorological factors of the 50 years.Moreover,geographic information data like vector diagram of 1:250 000 Hainan administrative region boundaries were used.

Research methods

The suitable growth probability,chilling damage probability,high temperature probability and comprehensive probability of TGMS rice during fertility sensitive period and heading flowering period under recent 50 years’ meteorological conditions were counted.Based on GIS technology,using Inverse Distance Weighting(IDW),spatial interpolation calculation was carried out for comprehensive probability,to objectively reckon the distribution conditions of regionalization indexes in non-observation stations,finally,we drew refined climatic zoning map of TGMS rice breeding.

Results

Two safety periods for the breeding

of TGMS rice

Rice is a warm season crop,chilling damage often leads to the delay of rice growth period and the increase of sterile grain rate.It is generally acknowledged[13]that in fertility sensitive period,when daily mean temperature＜20 ℃or daily minimum air temperature ≤17 ℃,the physiological effect of rice will be hindered and pollen can’t develop normally,thus tending to form empty or deformed grains; if the temperature continues to lower,growth days will be extended and the damage will be aggravated.If low temperature occurs in rice headingflowering period,at best,the phenomena of wrapround spikelet and black rice hull will happen,at worst,it will inhibit the normal growth of pollen grain,making material metabolism disordered,some of these injured pollen grains still can complete germination and fertilization,but the fertilized grains can’t further develop,thus empty grains will still be formed,generating “erect ears of rice” phenomenon.To determine the suitable regions and seasons of two-line hybrid rice breeding,we should based on two safety periods,namely,the safety periods of TGMS rice during fertility sensitive period and heading-flowering period,the two safety periods have some specific requirements for weather conditions and at the same time interrelate with each other.

Analysis on safety probability of TGMS rice breeding according to climate

Analysis on safety probability of TGMS rice breeding during fertility sensitive periodIn fertility sensitive period of TGMS rice,temperature is the most important meteorological indicator of breeding,determining the fertility restoration of TGMS rice.When breeding in natural conditions,because of narrow fertile temperature range of TGMS rice,moreover,it is easy to suffer abnormal high temperature or low temperature exceeding fertile temperature range,thereby causing breeding failure.Although there are certain differences in temperature susceptibility indexes of different twoline hybrid rice during fertility sensitive period,considering the uniformity of population development,the temperature conditions during fertility sensitive period are:daily average temperature is greater than or equal to critical sterile temperature (16 ℃),average temperature is no more than initial sterile temperature (usually 23 ℃)for 3 consecutive days[15].According to the research results,10-day average temperature of 17-23 ℃is the safety period during fertility sensitive period,if the 10-day average temperature is outside the range of 17-23 ℃,it is unsuitable condition.

The spatial distribution probability of meteorological factors of TGMS rice during fertility sensitive period from early January to early March was counted (as shown in Table1).From this,the safety probability of TGMS rice during fertility sensitive period gradually increased from south to north,and the maximum probability value of south reached 98%,however,the maximum value of north even can’t reach 80%;in the aspect of time,the probability of northern regions increased with the time,but the probability of southern regions was just the opposite,in which the probability decline of Sanya was the most obvious.The main reasons were as follows:low temperature occupied most of early fertility sensitive period,and the probability was during 32%-54%;in later period,high temperature enveloped southern regions,and the frequency even reached 54%.

Analysis on safety probability of TGMS rice breeding during heading-flowering period

In headingflowering period of rice,excessively high or low temperature both affected rice flowering and fertilization,thereby generating the decline of setting per-centage.Heading-flowering period of TGMS rice is over 10 days,therefore,10-day average temperature within the range of 22-33 ℃was the safety period of heading-flowering period in the paper,and outside the range was unsuitable condition.As shown in Tablemained at a higher level,and that of northern regions also increased,but that of western regions declined from a higher level (above 90%) to less than 50%.The main causes were:in early period,the probability of low temperature in northern regions was higher,2,the safety probability of southern regions during most of early headingflowering period exceeded 90% most of the time,and that of northern regions during January - February was lower than 60%; in later period,the probability of southern regions still re-and greater than that of 26%-74% in western and southern regions; in later period,the probability of low temperature in the whole province declined,conversely,the probability of high temperature increased,especially in inland regions of northwest and middle regions,such as Baisha and Changjiang,abnormal high temperature even reached 44% and 66%,respectively.

Table1 Meteorological conditions of TGMS rice during fertility sensitive period %

Table2 Meteorological conditions of TGMS rice during heading-flowering period %

Table3 The safety probability of meeting the needs of the two key periods %

The safety probability of meeting the needs of the two key periodsThe sensitive stage of fertility transition is generally 10-25 d before heading[12],therefore,not only the safety period of fertility transition,but also whether the temperature within 20 d after the safety period of fertility transition can meet the requirement of heading-flowering,should be considered.Hence,the probability of meeting the needs of the two safe periods was calculated by multiplying the probability of safety period of heading-flowering period with the probability of safety period of the first two ten-day sensitive periods.From Table3,the comprehensive probability of meeting the needs of the two key periods in northern regions,northeast part and middle regions was lower,and rarely exceeded 65%; however,in southern regions,the probability was the highest,especially the flowering phase was arranged during late January-early March,the probability of safety period was more than 80%,if the flowering phase was arranged after early March,the probability of the two declined obviously.These were consistent with the time of Hainan TGMS rice breeding,a lot of breeding experts[5]arranged fertility sensitive period in early and middle February,and heading-flowering period in late February and early March.

Division Results

The cumulative probability values of safety period,which met fertility sensitive period and heading-flowering period of TGMS rice,were interpolated and superposed together in GIS software platform,to calculate the marks.Then climatic regions for Hainan twoline hybrid rice were divided into three regions according to a descending order:suitable planting regions with the maximum value of ＞85%,subordinate suitable planting regions with the value of 65%-85% and unsuitable planting regions.Based on this,climatic regionalization thematic map of TGMS rice was made(see Fig.1),and we can see from the map that the climate suitability of hybrid rice basically presented zonal distribution from south to north,namely in the rank of suitable,subordinate suitable and unsuitable planting regions.

Suitable planting zones

Suitable planting zones mainly include Lingshui,Baoting Basin,Sanya and parts of low areas of Ledong,these regions had higher probability of safety period during fertility sensitive period and heading-flowering period of TGMS rice,and the probability of low temperature anomaly and high temperature anomaly was the minimum,these were also the places with the best heat conditions in the whole province,so these areas have had the largest rice planted areas at present,especially in Lingshui regions.Rationally arranging fertility sensitive period can improve yield and ensure quality,for example,late February was the safe period for fertility sensitive period,if after March,high temperature will cause breeding failure.

Subordinate suitable planting zones

Subordinate suitable planting zones mainly consist of Dongfang,parts of Changjiang,Wanning and parts of Wuzhishan,the probability of safety period in these regions during fertility sensitive period and headingflowering period of TGMS rice declined obviously comparing with suitable planting zones,and breeding damage was serious,these places had better heat conditions in the whole province.Eastern areas of the zones had better water conditions,conversely,western areas had the worst water conditions in the whole province,especially in winter and spring,the drought was severe,a lot of field management work like irrigation must be done.

Unsuitable planting zones

These zones mainly contain northern and central mountainous areas,which cover most parts of Hainan Island,the probability of safety period in these regions during fertility sensitive period and heading-flowering period of TGMS rice was the lowest;during the breeding period of hybrid rice,it was mainly affected by low temperature anomaly,if breeding in winter,chilling damage was severer;after late February,high temperature anomaly appeared rapidly,so breeding damage was also the most serious,thus the failure rate was higher,moreover,mountainous areas had less boundless paddy fields,the traffic was not convenient,so forestry economic crops were mainly planted in terrace.

Conclusions and Discussions

(1) Using GIS technology and refined net model analysis,the paper divided Hainan TGMS rice breeding into such three zones as suitable planting zones,subordinate suitable planting zones and unsuitable planting zones.The divisional results were more detailed,more accurate,and closer to actual distribution,which provided scientific basis for further optimizing breeding layout.

(2)The probability of safety period during fertility sensitive period of TGMS rice,geographically,increased gradually from north to south; in time,increased with time from early January to middle February,after late February,the probability declined.The main reasons were as follows:northern Wushishan was mainly affected by low temperature anomaly before middle February,afterwards,both low and high temperature anomaly were severe.Conversely,the probability of low and high temperature anomaly in southern Wushishan was lower,thus fitting for hybrid rice breeding.

(3)The probability of safety period during heading-flowering period of TGMS rice also increased gradually from north to south,and that of northern Wushishan was lower,most parts were affected by low temperature anomaly.At present,the planting area of cucurbits and vegetables in winter in southern Hainan was expanded,so the planting area of TGMS rice was restricted for the limited land.This study selected broader indicators of safety period during fertility sensitive period and heading-flowering period of TGMS rice,to provide certain guiding significance for scientifically choosing TGMS rice breeding bases,rationally carrying out allocation of production and time arrangement,and fully taking advantage of Hainan climatic resources,thereby reducing breeding risk to the maximum extent,and maximizing the benefit of hybrid rice breeding.

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