Effect of Sowing Date of Resistant and Susceptible Faba Bean, Vicia faba L. Cultivars on Orobanche crenata Forsk Seed Bank and Faba Bean Production

: The broomrape , Orobanche crenat a Forsk (Orobanchaceae) is a serious annual parasitic weed that causes considerable losses in many major crops including faba bean (Vicia faba L.). In Egypt: losses due to O. crenata parasitism may reach 40 to 100%. Despite using several methods to control O. crenata, success has not been achieved. The impact of different control tactics on O. crenata is not well understood . However, Sowing date appears to be one of the potential solutions for controlling O. crenata . In this work we investigated the effect of sowing dates on both the level of infection by O. crenata and the pod yield of faba bean using resistant (Giza 843) and susceptible (Nubaria 1) faba bean cultivars in naturally Orobanche infested soil. Moreover, the Orobanche seeds production was determined as an indication of seed bank future adding in soil. Under Orobanche free conditions, Nubaria 1 cultivar produces more pod yield than the resistant cultivar. The results demonstrated that, late sowing (3 weeks after normal sowing date) reduced significantly the number of emerged O. crenata shoots for both the resistant and the susceptible cultivars., Late sowing similarly contributed to a significant increase in pod yield (dry weight (kg)/plot) especially for Giza 843 (5.15 ± 0.02 Kg /plot), the resistant cultivar, which produced much higher pod yield than the susceptible Nubaria 1 cultivar (2.98± 0.06 Kg /plot) during the first season (2019 - 2020). During the second season (2020 - 2021), the pod yield was (3.85 ± 0.10) and (5.49± 0.76) Kg/plot for Giza 843 and Nubaria 1 cultivars, respectively, compared with the early sowing date. Furthermore, regarding both seasons,


Introduction
Faba bean is widely consumed pulses in the Mediterranean region and represents the main source of protein for the majority of the population in Egypt.In Egypt, despite the self-sufficiency from this vital crop in the 1970's was estimated to be 115% [1], this figure has severely declined since the 1980's, recording 26.9% in 2020 [2].Therefore, Egypt has become the major importer of faba bean worldwide, obtaining 480,000-520,000 tons yearly from overseas [3].This decline in self-sufficiency is principally attributable to the reducing in the cultivated area from 152,000 ha in 1961 to a lower record of 32,500 in 2017, representing 79% decrease [4].This decline in the cultivated area could be attributed to the spread of the parasitic weed, Orobanche crenata Forsk (Orobanchaceae) and the high production costs compared with other winter crops such as wheat or berseem clover.O. crenata, a complete root parasite, poses an extreme threat to faba bean [5].Heavy O. crenata infestation level was reported in many faba bean fields.In Egypt; losses of O. crenata parasitism may reach 40 to 100% under heavy infestation, [6].The leguminous losses due to O. crenata infestation depend on varia-tion of dominant environmental factors, severity of infection, and sowing date [7].Broomrapes (Orobanche spp.) are parasitic achlorophyllous weeds totally dependent on the host for organic carbon, water and nitrogen [8].The seeds of these parasitic weed may remain dormant in the soil for many years until germination is stimulated by root exudates from a host plant and the climatic conditions become favorable.A single plant of Orobanche can produce over 100,000 seeds which can survive in the field up to 20 years [9].
Several strategies have been applied to control Orobanche spp.Physical, cultural, chemical and biological methods have been explored but none has proven to be sufficiently effective, economical and as applicable as desired [10].The efficacy of these control strategies has, often been affected by environmental conditions.
Planting date is an important on the intensity of O. crenata infection.Early plantings of faba bean, lentil, and peas are more severely infected.Unfortunately, delayed planting greatly reduces potential crop yield, but a compromise of a few weeks delay can be found for each particular crop and region, so the decrease in crop biomass is compensated by the reduction in the infection [11].In this work we studied the effect of sowing dates of faba bean cultivars on O. crenata infection and seed production in addition to faba bean production.

Materials and Methods
Field trials were conducted during two cropping seasons (2019/2020) and (2020-2021) in the Agriculture Experimental Unit of Nubaria Research Station.Two faba bean cultivars were used: Giza 843 resistant to O. crenata and the susceptible one Nubaria 1.These cultivars were sown in a sandy loam soil field naturally infested with O. crenata in 4 rows of 4 m length with 0.5 m row spacing and 50 seeds per row.Two sowing dates at 15 days interval starting from November 10 were evaluated, respectively, during both cropping seasons.No fertilisers or other chemical treatments were applied during both seasons.
A multifactor blocks design with 3 blocks was used.Each treatment was replicate four times with plot area 42m 2 .For the two seasons, the number of emerged Orobanche shoots and faba bean dry grain yield (kg/plot) were recorded at crop maturity stage on the two central rows of each plot.As well, the number of fruits and seeds /spike and spike length (cm) were recorded.
Statistical analyses: Means comparison of early and late sowing date for each response variable were performed using independent t-test by SPSS version 20 [12].

Results
The number and infestation percent of the emerged Orobanche shoots as well the dry pod weight (kg.)/plot, yield, of resistant (Giza 843) and susceptible (Nubaria 1) culti-vars at the maturity stage of faba bean are shown in Table 1.The results demon-strated that, late sowing reduced significantly the number of emerged O. crenata shoots for both the resistant and the susceptible cultivars.During the first season, the number of parasitic shoots /plot was 112.00 ± 6.31 for the early sowing date vs 79.00 ± 10.10 for the late sowing date of Giza 843 (t= 4.8, P < 0. 05) and 202.00 ± 2.60 for the early sowing date vs 100.00 ± 18.65 the late sowing date of Nubaria 1 (t= 9.3, P < 0. 05).The same trend was observed in the second season.
During the first season, pod yield increased significantly (t=99.9P < 0. 05) on late sowing dates for the resistant Giza 843 cultivar (from 2.67 to 5.15 kg/plot, in respect), which produces a much higher pod yield than the susceptible Nubaria 1 cultivar (t= 6.75, P < 0. 05) (2.98 kg/plot) during the first season.
As regards the susceptible Nubaria 1 in the second season (2020-2021), the analysis showed significant differences among sowing dates (t=6.2,P < 0. 05) for more dry pod weight per plot of grain yield (Table 1).
Table 2 shows the effect of sowing date of the tested cultivars on the spike length (cm) and capsules number and seed production of the parasitic weed, O. crenata.In most cases, late sowing date significantly reduced both of the spike length of Giza (t=3.4,P < 0. 05) and Nubaria (t=6.6,P < 0. 05) during the first season and in the second season for Giza (t=3.6,P < 0. 05) and for Nubaria (t=6.2,P < 0. 05), respectively.When the letter per each column is the same, the data for separately season is not significantly different (P< 0.05).
The number of spike fruits reduced in late growing season compared of those found in the first season.The consequences were significant reductions of new additions of seed bank (Figure 1) during late season sowing date.Cultivar of Giza 834 had less emerged O. crenata shoots than the susceptible one for both crop seasons.
Regarding Orobanche seed production, data in table 2 shows that, Orbanche seed production of emerged spikes in the late sowing faba bean significantly decreased compared with that in early sowing plots of both resistant and susceptible cultivars.For example, in the first season, there is a significant difference between seed number produced by the emerged Orobanche in late sowing Nubaria 1 cultivar plots (402,000 ± 120,00 seeds/spike) and the seed number that produced by the emerged Orobanche in the early sowing plots (589,000 ± 230,00 seeds/spike); [t = 22.28, p < 0.05].Like-wise, in the second season, Giza 843 showed the same trend since the seed number The number and infestation percent of the emerged Orobanche shoots as well the dry pod weight (kg.)/plot, yield, of resistant (Giza 843) and susceptible (Nubaria 1) cultivars at the maturity stage of faba bean are shown in Table 1.The results demonstrated that, late sowing reduced significantly the number of emerged O. crenata shoots for both the resistant and the susceptible cultivars.During the first season, the number of parasitic shoots /plot was 112.00 ± 6.31 for the early sowing date vs 79.00 ± 10.10 for the late sowing date of Giza 843 (t= 4.8, P < 0. 05) and 202.00 ± 2.60 for the early sowing date vs 100.00 ± 18.65 the late sowing date of Nubaria 1 (t= 9.3, P < 0. 05).The same trend was observed in the second season.
During the first season, pod yield increased significantly (t=99.9P < 0. 05) on late sowing dates for the resistant Giza 843 cultivar (from 2.67 to 5.15 kg/plot, in respect), which produces a much higher pod yield than the susceptible Nubaria 1 cultivar (t= 6.75, P < 0. 05) (2.98 kg/plot) during the first season.
As regards the susceptible Nubaria 1 in the second season (2020-2021), the analysis showed significant differences among sowing dates (t=6.2,P < 0. 05) for more dry pod weight per plot of grain yield (Table 1).
Table 2 shows the effect of sowing date of the tested cultivars on the spike length (cm) and capsules number and seed production of the parasitic weed, O. crenata.In most cases, late sowing date significantly reduced both of the spike length of Giza (t=3.4,P < 0. 05) and Nubaria (t=6.6,P < 0. 05) during the first season and in the sec-ond season for Giza (t=3.6,P < 0. 05) and for Nubaria (t=6.2,P < 0. 05), respectively.
The number of spike fruits reduced in late growing season compared of those found in the first season.The consequences were significant reductions of new additions of seed bank (Figure 1) during late season sowing date.Cultivar of Giza 834 had less emerged O. crenata shoots than the susceptible one for both crop seasons.
Regarding Orobanche seed production, data in table 2 shows that, Orobanche seed production of emerged spikes in the late sowing faba bean significantly decreased compared with that in early sowing plots of both resistant and susceptible cultivars.For example, in the first season, there is a significant difference between seed number produced by the emerged Orobanche in late sowing Nubaria 1 cultivar plots (402,000 ± 120,00 seeds/spike) and the seed number that produced by the emerged Orobanche in the early sowing plots (589,000 ± 230,00 seeds/spike); [t = 22.28, p < 0.05].Like-wise, in the second season, Giza 843 showed the same trend since the seed number significantly reduced from 229,000 ± 10 seeds/spike in early sowing plots to 169,000 ± 80 seeds/spike in late sowing plots; [t = 25.69,p < 0.05].This study investigated the effect of sowing date on O. crenata infection level and seed bank employing two faba bean cultivars (resistant and susceptible).The level of infestation by Orobanche was higher throughout the first season than that recorded within the second one probably due to a satisfactory environmental condition in particularly milder winter and dry season which ensuring the attribution of the environmental conditions on the parasitism by Orobanche as reported by previous studies.[13,14].Delayed sowing has been reported to cause reduction in O. crenata infection [13,15].Another study reported that, early sowing can lead to high crop losses as a consequence of higher infection levels and longer exposure to the parasitic weed [16].
In our study, late sowing dates (November 25) resulted significant reduction in the number fruits of emerged O. crenata as well as the dry weight of spike shoots for the resistant faba bean cultivar in the first season but not in the second season.The resistant cultivar demonstrates a better control of O. crenata weed infestation with delayed sowing.The reduction of Orobanche infection with delayed sowings could be due to the inducing of a secondary dormancy in Orobanche seeds, the temperature effects on germination and/or obstructing of Orobanche development during underground stages [16,17,18].While delayed sowing could have negatively impact on the yield of certain legumes that have a long-life cycle [19,20], Results of our study demonstrated that, according to the measurements of crop yield over two growing seasons, delayed sowing resulted in higher seed yield per plot for both cultivars (especially Giza 843).On the other hand, Pérez-de-Luque [11] reported that, the resistant cultivar usage enables an early sowing and a extended crop cycle, with minute of O. crenata development, and higher crop production.The employing of a resistant cultivar such as Giza 843 represents a respected control solution and could be a beneficial tool for an integrated pet management tactic leading to regain soil with lover level of infestation by Orobanche.However, some precautions should be considered to reduce the hazard of developing more virulent ecotypes.Cultivating a susceptible faba bean cultivar in extremely infested field with delayed sowing did not achieve a satisfactory grain yield.Therefore, other control methods, such as chemical treatment should be employed to reduce the infestation levels.

Conclusion
Broomrape weed infestation is the principal factor that affecting faba bean production.While integrated weed management is the most known strategy for control the broomrape, the culture practice is the foremost phase for successful control.Sowing timing and suitable cultivar are vital tactics to avoid undesirable conditions and pests.In this work we emphasized the importance of binary effects of different control components.Integrating both delayed sowing and resistant cultivar could be a valuable tool as a component of an integrated weed management strategy to control O. crenata in faba bean fields.Moreover, this study highlights the beneficial of both resistant cultivar and delayed sowing for reducing the seed bank of O. crenata which might be allow regain the areas where farmers could not cultivate beans as a result of high level of seeds in the soil.However, Further research is required to determine the long-term effects of these measures on O. crenata seed bank.

Figure 1 .
Figure 1.Effect of sowing date on parasite seed bank.

Table 1 .
Effect of sowing date of two faba bean cultivars on number, infestation rate of O. crenata and pod yield (dry weight kg./plot) of faba bean.When the letter per each column is the same, the data for separately season is not significantly different (P< 0.05).

Table 2 .
Effect of sowing date of two faba bean cultivars on length (cm), capsules number and seed production of parasitic weed, O. crenata.