# Alternaria Black Spot (_Alternaria brassicae_) Infection Severity on Cruciferous Oilseed Crops
## 4 Discussion
A higher tolerance of 35-day old cruciferous plants to _A. brassicola_ compared to the 45- or 55-day-old plants is another possible reason why _R. sativus_ and _E. sativa_, both in an earlier growth phase, were more resistant to the _Alternaria_ black spot disease than _B. napus_, _B. nigra_ and _B. juncea_, which were in a more advanced growth phase (Figure 1, Tables 1 and 2) [37]. In 2020, [PERSON] et al. [38] showed that due to lower foliar contents of protective and antifungal polyphenolic compounds and glucosinolates, the older _B. juncea_ leaves had a considerably greater _A. brassicola_ damage than the younger leaves. A similar result was obtained by [PERSON] et al. (2011) [39], who compared different plant genotypes with varying susceptibility against _Alternaria_ black spot disease and found that, compared to _B. juncea_ as the most susceptible species, the resistance of _B. alba_ was related to higher content of phenolic compounds in the leaves. Nevertheless, there is evidence that during the infection, the contents of antifungal phenolic compounds increase [38], but the capacity for accumulation of protective compounds might decrease with increasing leaf age and onset of leaf senescence. As discussed above, higher temperatures promote the Alternaria black spot disease development. Thus, climate warming could directly enhance the risk for Alternaria black spot pressure on cruciferous species, including oilseed crops [33], and might increase the yield gap. Similarly, in the Northern Baltics, recent unusually warm summers have increased the spread of _Alternaria_ spp. on potato fields and led to severe infections [24; 40]. In addition, the predicted increase in the frequency of warmer and drier summers with temporary heat waves [41] could increase problems due to _Alternaria_ spp. pathogen spread, damage and Alternaria black spot disease control in Northern regions. Recent research has shown that in the Baltic Sea region, the climate has warmed particularly fast compared to the global average [42]. In the current study, Alternaria black spot disease infection was high on half of the tested cruciferous species, and we consider that this pathogen constitutes a direct threat to oilseed crops. Altered climatic conditions for plant growth due to global change and the growing population of the world reinforce the development of strategies for a sustainable agriculture and food system that ensure the efficient land use and high nutritional value of plants [43]. Thus, the knowledge of Alternaria black spot spread and plant vulnerability allows selection of more resistant species and cultivars, and this information is highly relevant for oilseed, intercrop, cover crop and green manure production, especially in sustainable farming systems. Currently, there is a limited assortment of alternative cruciferous and non-cruciferous oilseed crops for cultivation in upper latitudes, and there is a strong demand for new oilseed crops by local producers [44]. Alternative cruciferous species should be recommended for cultivations as green manure, intercrop, oilseed or for trap crop only if their susceptibility to Alternaria black spot is examined/known in a certain region. In the case of use of susceptible cultivars, one should carefully assess whether the losses do not exceed profits. Until this work, information about the Alternaria black spot disease climatic sensitivity and cruciferous crop resistance was not available for Northern Baltic region conditions. Based on our observations in two extremely warm growing seasons in the Northern Baltics, we suggest that under favorable conditions for Alternaria black spot infection, alternative oilseed crops such as _S. alba_, _E. sativa_ and _R. sativus_ possess a great potential to grow with limited chemical inputs even in the case of conventional farming. The results of this work can be harnessed by local organic and sustainable farmers, who have already started to cultivate alternative cruciferous crops such as _B. juncea_, _S. alba_ and _R. sativus_ as intercrop and green manure.