THE INFLUENCE OF ENVIRONMENTAL FACTORS ON FLOWERING OF FRENCH BEAN ( PHASEOLUS VULGARIS L . )

Observations of major development stages and fl owering of four French bean (Phaseolus vulgaris L.) cultivars cultivated for green pods from six sowing dates (since mid of May till end of June) at weekly intervals were performed in 2003-2005. The study included the determination of the number of infl orescences per plant, number of fl owers in infl orescence, length of infl orescence axis, and number of total and marketable pods per plant. French bean sown in the mid of May till the end of June showed the greatest variability with respect to the fl owering start date and fl owering period length as well as the number of pods set on a plant. French bean plants sown on different dates produced a similar number of infl orescences and fl owers per bunch; 61.6-74.6 fl owers per plant, on average. Weather conditions in July and August had the greatest infl uence on the fl owering pattern and bean pod setting.


INTRODUCTION
Bean (Phaseolus vulgaris L.) is cultivated in Poland for dry seeds and immature pods, i.e. as green bean -French bean (snap bean), which in general affects the crop technology of used cultivars.
French bean, due to a short vegetation period, may be cultivated with the sowing beginning from mid May till the end of June, which allows the pod harvest period to be extended to six-seven weeks when selecting only several cultivars.Environmental conditions, mainly air temperature and rainfall, greatly affect the growth and development of bean plants as well as they shape the plant's morphological traits and productivity  2006) reveals that snap bean sown in spring in a polyethylene unheated plastic tunnel showed worse pod setting on a plant and a shorter fl owering period at air temperatures above 30-35°C at the stage of generative development.
When cultivated on a fi eld under moderate climate conditions, common bean is more frequently exposed to low air temperatures, which infl uences fl ower and pod fading and dropping (G e o r g e , 1999).
In studies on factors determining the bean fl owering, W a l l a c e et al. (1991) found that there was quite high interdependence between day length, temperature and cultivar traits.The optimum temperature for bean fl owering at daily light of 12 hrs was 27°C, whereas the extension of daylight hours to 18 h allowed the optimum temperature for the bean plant fl owering to be decreased to 18°C.
This paper aims to evaluate the infl uence of six dates of French bean sowing at about weekly intervals since mid May till the end of June, on the course of major development stages, fl owering abundance, and pod setting.

MATERIALS AND METHODS
The studies were conducted in 2003-2005 at the Experimental Farm Felin, University of Agriculture in Lublin, Poland.
Experimental material consisted of four French bean cultivars: Paulista and Hit -green-pod as well as Korona and Galopka -yellow-pod.Six sowing dates were applied: mid of May, end of May, May/June, beginning of June, mid of June, and end of June.
The double-factor experiment was set by means of randomized blocks in 4 replications.Each plot was of 4.05 m 2 in area (3 m long and 1.35 m wide).Plants were sown in three rows at 0.45 m×0.08 m spacing on every plot.Fertilization and nursery operations were made in accordance with common recommendations for bean plants.
Observations were made of the course and length of major development stages together with fl owering and pod setting for four bean cultivars cultivated from mid-May till the beginning of September.
Using 10 randomly selected plants (2-3 replications), the following items were determined: number of infl orescences per plant, number of fl owers per infl orescence, length of infl orescence axis, and number of pods set on a plant -total and marketable.
The characteristics of weather conditions are presented on the basis of data obtained from the meteorological center at the Department of Agrometeorology, University of Agriculture in Lublin, located at the Experimental Farm Felin.
Measurement results were statistically processed by means of variance analysis and using Tukey's confidence intervals at the signifi cance level of α = 0.05.

RESULTS
French bean plants manifested signifi cant variability with respect to the start date and the length of particular development stages depending on the sowing date, cultivar and study year (Tab.1).
In general, thermal conditions in 2003-2005 were more favorable than average ones in that area (Tab.2).
The fl owering stage -for various sowing dates -was observed from the end of June till the beginning of August, i.e. 28-42 days after emergence.The start of fl owering of bean plants sown in mid-May occurred 37 days after emergence (the longest period), and the fl owering started the earliest (32 days after emergence) in the plants sown at the end of May and beginning of June (Tab.3).
The pattern of climatic factors in 2004, when air temperature since May till the end of June was lower as compared to long-term mean values, resulted in the delayed start date of fl owering (42-43 days after emergence) for plants sown on the fi rst dates.In 2003, when higher temperatures were recorded in May (by 3.2°C), June (by 0.9°C) and July (by 1.9°C), the earliest fl owering start was observed for bean plants sown in May (25-29 June), i.e. 30-32 days after emergence.
The length of the fl owering stage for bean plants changed fi rst of all due to the sowing date; it was 16--30 days during the study.The fl owering period was the shortest for the earliest sown plants (19 days) and the longest (25 days) for bean plants with the sowing date in mid-June.Differences in fl owering period length reached 6 days: the longest period (25 days) occurred in the cooler year 2004, the shortest one (19 days) under the conditions of high temperatures and insuffi cient rainfall during plant fl owering in 2003 (Tab.3).
Potential yielding abilities of legumes, including bean, depend not only on fl owering period length, but also fl owering abundance and the number of pods set on a plant.
The number of infl orescences per plant and fl owers per infl orescence showed signifi cant differences depending on the variety, sowing date and year of study.On average, the highest number of fl owers was found for plants sown on the fi rst three sowing dates (from mid-May till the beginning of June).The number of fl owers per infl orescence from the plants sown at the earliest date was signifi cantly the lowest.Mean fl ower number per plant was the lowest in the plants sown late, in the middle and end of June (61.6-62.4)(Tab.4, Fig. 1).
In the cooler year of 2004, bean plants produced a signifi cantly lower number of infl orescences, but the number of fl owers per infl orescence was higher.Bean infl orescences produced in 2004 were characterized by a signifi cantly longer infl orescence axis (20.1 cm) as compared to those grown under higher temperature conditions in 2003 -they were three times shorter, on average.
The different sowing date for snap bean exerted a signifi cant infl uence on the number of total and marketable pods set (Fig. 1).The signifi cantly lowest number of total pods was found on the plants from the earliest and latest sowing dates, i.e. sown in the middle of May and the end of June (19.8 and 20.8,respectively).The number of marketable pods per plant was signifi cantly the lowest from the earliest sowing date (12.4 pods, on average).
A comparison of six sowing dates of snap bean -from the middle of May till the end of June -reveals that fl owering abundance was at similar levels, but pod setting was characterized by signifi cant variability.

DISCUSSION
Common bean, as a thermophilic plant, requires 18-25 °C for its proper growth and development.In fi eld cultivation, the sowing should be made at about mid-May, when the risk of spring frost is zero.However In the moderate climate, fi eld plantations of bean are not exposed to long-lasting high temperatures.However, this phenomenon may occur in cultivations under polyethylene cover, which was confi rmed by earlier studies by Ł a b u d a et al. (2006).The research reveals that the fl owering period for bean plants cultivated in the high plastic tunnel, where mean daily air temperature ranges from 20.4°C to 27.3°C, was 25-32 days, while at 11.4-22.4°Cand on the fi eld -up to 31-37 days.The number of pods set on a plant was 13-22, and 24.5-35.5 in the plastic tunnel and on the fi eld, respectively.G r o s s and K i g e l (1994) found that the poorest pod setting was observed for common bean exposed to high temperatures 1-6 days before fl owering.The study of I b a r r a -P e r e z et al. (1999) reveals that poorer pod setting on common bean (as a self-pollinating plant) may occur in the absence of pollinating insects, which was proven for some dwarf cultivars.
Flower and pod falling is a common phenomenon, which may result from insuffi cient fl ower pollination, depending on genetic background, or be an effect of different availability of plant-origin assimilates and hormones.At higher soil humidity and with shortened daylight hours, plants produce many fl owers, but only 7-12% of them set pods.With a lower soil moisture content and longer daylight hours, plants form a lower number of fl owers, but 17-24% of them produce pods, and therefore the yield is higher (P r u s i ń s k i and B o r o w s k a , 2002).
It follows from the present study that the number of total pods on French bean plants sown at various dates from 19.8 (mid-May sowing) to 26.7 (end of May and beginning of June sowing).The fl owering period of French bean varied, mainly depending on the sowing dates and study years, amounting from 16 to 29 days.Differences in fl owering period lengths for plants sown on different dates were 2-6 days, while with respect to the studied cultivars 1-2 days.
(S z y r m e r et al. 1992; G r o s s and K i g e l , 1994; M o u h o u c h e et al. 1998; I b a r r a -P e r e z et al. 1999).THE INFLUENCE OF ENVIRONMENTAL FACTORS ON FLOWERING OF FRENCH BEAN (PHASEOLUS VULGARIS L.) Helena Łabuda, Anna Brodaczewska Department of Vegetable Crops and Medicinal Plants, University of Agriculture in Lublin, Poland 20-068 Lublin, Leszczyńskiego 58 e-mail: helena.labuda@ar.lublin.plResearch conducted by Ł a b u d a et al. ( , as reports reveal (S u m m e r f i e l d and R o b e r t s , 1984; M o n t e r r o s o and W i e n , 1990; S u z u k i et al. 2001), bean plants are characterized by susceptibility to high temperatures during their generative growth.The negative infl uence of prolonged high temperature (27-35 °C) during fl owering on pod setting was proven as well.

Table 3
Period of fl owering of French bean cultivars from different sowing dates.Mean decade air temperature (˚C) and total rainfall (mm) in 2003-2005 (experimental fi eld, Felin-Lublin).The development stages of French bean growth depending on the sowing date (mean for cultivars).

Table 4
Characteristics of fl owering of French bean cultivars from different sowing dates.sowing date (end of June).Weather conditions in July and August had the most signifi cant infl uence on fl owering and pod setting in French bean. late